Method of evaluating characteristics of a light beam, apparatus for evaluating the characteristics, and apparatus for adjusting a write unit by employing the evaluation method

ABSTRACT

At least two light beam detection units are spaced at a predetermined distance and provided in the scanning direction of a surface to be scanned. A light beam is emitted to the light beam detection unit provided on a scanning start side, by lighting a light beam source which is employed to scan the surface linearly during a scanning period equivalent to 1 dot during scanning. A light beam is emitted to the light beam detection unit provided on a scanning end side, by lighting the light beam source during the scanning period after elapse of a light-off period computed from a previously designed scanning speed and the predetermined distance. Based on a detection result of the light beam detection unit provided on the scanning start side and a detection result of the light beam detection unit provided on the scanning end side, scanning characteristics required of the light beam are evaluated.

This application is a Division of application Ser. No. 09/104,386 filedon Jun. 25, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for evaluating an imageformation device, such as a laser printer and a copying machine. Moreparticularly, the invention relates to a method of evaluatingcharacteristics required of a light beam which is emitted from the writeunit of an image formation device toward a latent image carrier, such asa photosensitive drum and a photosensitive belt. The invention alsorelates to a light beam characteristic evaluation apparatus that isemployed for evaluating the characteristics, and further relates to anapparatus for adjusting a write unit by employing the evaluation method.

2. Description of the Related Art

Conventionally, an image forming device, such as a laser printer, acopying machine, and a facsimile device, performs writing on the surfaceof the photosensitive drum (latent image carrier) of an image formingunit by scanning the drum surface in both a horizontal scanningdirection (i.e., main scanning direction) and a vertical scanningdirection (i.e., sub-scanning direction) with a light beam emitted froma write unit, thereby forming an electrostatic latent image. In order tomake the latent image visible and form a toner image, toner is caused toadhere to the surface of the photosensitive drum on which the latentimage is formed. The toner image is transferred and fixed onto transferpaper. In this manner, an image is formed on the transfer paper.

The write unit is provided with an optical scanning system for scanningthe surface of the photosensitive drum with a beam of light. The surfaceof the photosensitive drum is scanned in the horizontal scanningdirection by the optical scanning system, while the surface is scannedin the vertical scanning direction by rotating the photosensitive drum.

In these image formation devices, incidentally, the characteristicsrequired of the light beam of the write unit are evaluated in performingwriting on the surface of the photosensitive drum which is a writingobject.

For instance, in a copying machine, the image information on amanuscript is read in sequence and converted to a beam of light. In thecase where the light beam writing position on the photosensitive drumsurface deviates from a previously designed reference position, therearises a disadvantage that an image corresponding to the imageinformation of a manuscript cannot be formed at the reference position.Particularly, in an image formation device, in which two laser lightsources for emitting a beam of light are provided in the write unit andwriting is performed on the photosensitive drum surface at two times thenormal speed by scanning the photosensitive drum surface in thehorizontal scanning direction concurrently with two light beams, if thewriting position of one of the two light beams deviates from the writingposition of the other light beam in the horizontal scanning direction,the image on a manuscript cannot be reproduced with high fidelity.Therefore, it is required to perform both the evaluation of the writingposition of one light beam and the evaluation of the writing position ofthe other light beam.

In the case of a write unit which performs writing on a photosensitivedrum by a single light beam, a writing position is computed for eachsurface of a polygon mirror constituting an optical scanning system. Theobject of evaluation in this case is both the position offset in thehorizontal scanning direction (pitch fluctuation in the horizontalscanning direction) on each surface of the polygon mirror and theposition offset in the vertical scanning direction (pitch fluctuation inthe vertical scanning direction) on each surface of the polygon mirror.

In the case of a write unit which performs writing on a photosensitivedrum by a plurality of multiplexed light beams, a pitch between lightbeams is also an object of evaluation in addition to the aforementionedevaluations.

Also, when two points on a manuscript in the horizontal scanningdirection are extracted, two points on a copied image on transfer papercorresponding to the two points on the manuscript are extracted, and thedistance between the two points on the manuscript is compared with thedistance between the two points on the copied image, they must be equalto each other as long as copying is performed with equimagnification. Ifthe distance between two points on a manuscript is not exactly equal tothe distance between two points on a copied image, this will result in amagnification error. Since an image cannot be reproduced with highfidelity on transfer paper, performing the evaluation of a magnificationerror is required. In addition, in the case of enlargement andreduction, a ratio of a copied image formed on transfer paper to animage on a manuscript has to be equal to a desired magnification ordemagnification ratio. If these ratio differ from each other, an imagecannot be reproduced with high fidelity and therefore the evaluation ofa magnification error will also be required.

Additionally, in the case where a left-side point and a right-side pointon transfer paper are offset in the vertical scanning direction, itmeans that the scanning line has a tilt to the left or the right andtherefore this scanning line tilt is also an object of evaluation.

Furthermore, assume that three points on a manuscript are extracted fromleft to right along the horizontal scanning direction and that themiddle point is present at equal distances from the remaining twopoints. If the distance to the corresponding left-side point and thedistance to the corresponding right-side point on the transfer paper arenot equal with the corresponding middle point on the transfer paper asreference, a copied image will lack the balance between the right sideand the left side. Therefore, it is also required to evaluate whether ornot a distance from a middle point to a left-side point and a distancefrom a middle point to a right-side point are equal to each other.

In this case, if the difference between the writing position of theleft-side point and the writing position of the middle point is notequal in the vertical scanning direction to the difference between thewriting position of the right-side point and the writing position of themiddle point, the scanning line will have a curve. Similarly, an imageis not reproduced with high fidelity, so that it is also required toevaluate whether or not a scanning line has a curve.

Incidentally, a conventional apparatus for evaluating thecharacteristics of a light beam in the horizontal scanning direction isshown, for example, in FIG. 1 (see Japanese Laid-Open Patent PublicationNo. HEI 5-284293).

In the figure, reference numeral 1 denotes a write unit (optical unit).The write unit 1 is provided with a beam source (laser light source) 2,a rotatable polygon mirror 3, and an f θ lens 4. The beam source (laserlight source) consists of a semiconductor laser 2. The semiconductorlaser 2 is modulated and driven by an optical analog modulator 5. Theoptical analog modulator 5 modulates the strength of laser light emittedfrom the semiconductor laser 2 in correspondence to a manuscript image.The laser light emitted from the semiconductor laser 2 is deflected byrotation of the polygon mirror 3.

A pair of spaced photoelectric conversion elements 7 a and 7 b areprovided in the horizontal scanning direction on a photosensitivesurface 6 equivalent to the surface of a photosensitive drum provided inan image forming unit. In order to enhance received-light positionaccuracy (writing position accuracy), light intercepting plates 8 a and8 b with a pinhole (circular small hole) are provided directly beforethe photoelectric conversion elements 7 a and 7 b. Let the distancebetween this pair of pinholes be L.

If the polygon mirror 3 is rotated with the semiconductor laser 2 lit atall times during scanning and if the photosensitive surface 6 is scannedin the horizontal direction Q1 with the light beam P1, the firstphotoelectric conversion element 7 a will first receive the light beamP1 and then the second photoelectric conversion element 7 b will receivethe light beam P1. From the difference between the light receiving timesand the distance L, an actual scanning speed of the light beam P1 ofthis write unit 1 can be computed. When this actually measured scanningspeed of the light beam P1 is faster or slower than a previouslydesigned scanning speed, the writing position of the light beam P1 isoffset from the writing reference position.

Hence, whether this actually measured scanning speed of the light beamis within the allowable error of the designed scanning speed isevaluated. In the case where the measured scanning speed has exceededthis allowable error, the revolution speed of the polygon mirror 3 isadjusted so that the scanning speed of the write unit is within theallowable error.

This conventional light beam characteristic evaluation apparatus cannotcompute the writing position itself directly. If it is to be computed,time needs to be computed until an output signal is output from thesecond photoelectric conversion element 7 b since an output signal wasoutput from the first photoelectric conversion element 7 a. In addition,an actual scanning speed needs to be computed by dividing the distance Lwith the computed time, and a computation for converting this scanningspeed to a writing position is needed. Therefore, the procedure forcomputing the writing position becomes complicated. Also, thecharacteristics of the light beam to be evaluated are limited.

Next, in the case where the beam diameter of the light beam P1 on thesurface of the photosensitive drum is offset from a previously designedvalue, the edge of an image formed on transfer paper will become dim, orcracks will occur in the scanning line, so that there is a disadvantagethat picture quality will be degraded. Therefore, it is also required toevaluate the diameter or shape of the light beam on the scanned surface.

In a conventional method of evaluating the beam diameter of a lightbeam, a pinhole or a slit is provided at a position corresponding to thesurface of a photosensitive drum, and a light receiving device isprovided directly after the pinhole or the slit. With this arrangement,the beam diameter is measured in a stationary state. This conventionalmethod, however, cannot measure the beam diameter in a scanning state.

Hence, in order to measure the beam diameter in a scanning state, amethod of and an apparatus for evaluating the beam diameter of a lightbeam have been proposed (see Japanese Laid-Open Patent Publication No.HEI 4-351928). As shown in FIG. 2, a one-dimensional (1-D) chargecoupled device (CCD) 9 is provided on the photosensitive surface 6equivalent to the surface of the photosensitive drum. In the opticalpath of the light beam P1 traveling toward the 1-D CCD 9, an objectivelens is provided for directing the light beam P1 onto the photosensitivesurface 6. While the beam spot S of the light beam P1 is being moved ina direction of arrow Q1 along the horizontal scanning direction, the 1-DCCD 9 is scanned n times in a direction of arrow Q2. The light quantitysignals of pixels C1 to Cn during a signal scan are integrated andstored in a storage circuit. By computing a signal from this storagecircuit, the light beam diameter is computed.

Incidentally, in this conventional evaluation method, when the 1-D CCD 9is moved once in the direction of arrow Q2 and then is moved again inthe direction of arrow Q2, the 1-scan period t1 of the 1-D CCD 9 haselapsed. For this reason, the light beam P1 has moved in the horizontalscanning direction (direction of arrow Q1) for this 1-scan period t1.Therefore, this evaluation method is equivalent to the constitution inwhich n 1-D CCDs 9 are arranged at regular intervals with the beam spotS in a stationary state, as schematically shown in FIG. 3.

In this evaluation method, as evident in FIG. 3, the light beam P1 hasmoved in the horizontal scanning direction for the 1-scan period t1 ofthe 1-D CCD 9, so that the beam spot S is fetched in a thinned-out statein the 1-D CCD 9. Furthermore, during the scanning period Δt between thetime that after a certain pixel Ci of the 1-D CCD 9 is scanned, theimage information is read and the time that after the adjacent pixelCi+1 is scanned, the image information is read, the light beam P1 alsomoves in the horizontal scanning direction (direction of arrow Q1).Therefore, this is equivalent to fetching an image of the beam spot S byobliquely scanning the 1-D CCD 9, so that an error easily comes to occurwhen the beam diameter is quantized. The evaluation error in thisquantization of the beam diameter is increased as the scanning speed ofthe light beam P1 is increased.

The aforementioned conventional light beam characteristic evaluationmethod (beam diameter evaluation method), therefore, has thedisadvantage that it is difficult to enhance the evaluation accuracy ofthe beam diameter.

As previously described, the characteristics required of the light beamare a writing position characteristic to a photosensitive drum surface,pitch fluctuation in a horizontal scanning direction, pitch fluctuationin a vertical scanning direction, a beam-to-beam pitch, a magnificationerror, right-left balance (magnification error deviation), a scanningline curvature, a light beam diameter, a beam shape, and so on. In priorart, since the beam characteristics are evaluated by exclusiveevaluation apparatuses, the characteristic evaluation of the light beambecomes complicated and is not a synthetic evaluation under the samecondition, so that there is a fear that reliability of evaluation willbe slightly reduced.

Furthermore, for a method of evaluating a beam spot diameter or a beamspot shape, there is a demand for an even greater enhancement in theevaluation accuracy of the beam spot diameter or beam spot shape in ascanning state.

In addition, positioning of a reference position is required in order toperform these evaluations.

For instance, Japanese Laid-Open Patent Publication No. HEI 8-86616discloses a three-dimensional (3-D) image measurement apparatus equippedwith a computer. This measurement apparatus is provided with a laserhead for emitting a cross-shaped slit light to an object of measurementhaving a 3-D shape. The laser head is provided on a laser head bed sothat it is rotatable on the intersection of the crossed slit and movablein a right-and-left direction and an up-and-down direction. Thismeasurement apparatus is further provided with a CCD camera forphotographing the measurement object, an image processing section forprocessing an image signal photographed by the CCD camera, and a laserhead operation control section. In this 3-D image measurement apparatus,the lens center of the CCD camera and the center portion of the pointend of the laser head are located on the X axis of a 3-D absolutecoordinate system, and the photographing surface of the CCD camera isarranged in parallel to the X-Y plane.

This image measurement apparatus merely performs positioning of thearea-type CCD element of the CCD camera by adjusting the area-type CCDelement at a specific position in correspondence to the photographingposition of the area-type CCD element and does not specify a referencepixel as a reference position for measurement. For this reason, there isa problem in that the offset between the positions of the referencepixel and laser light cannot be accurately grasped.

SUMMARY OF THE INVENTION

It is a first object of the present invention to provide a light beamcharacteristic evaluation method and a light beam characteristicevaluation apparatus which are capable of evaluating all characteristicsrequired of a light beam.

A second object of the present invention is to provide a light beamcharacteristic evaluation method and a light beam characteristicevaluation apparatus which are capable of evaluating the diameter orshape of a light beam accurately even during scanning in a horizontalscanning direction (i.e., main scanning direction).

A third object of the present invention is to provide a light beamcharacteristic evaluation apparatus which is capable of performingpositioning of a reference position accurately.

A fourth object of the present invention is to provide an adjustmentapparatus for a write unit which is suitable for performing adjustmenton the basis of results evaluated by employing the light beamcharacteristic evaluation apparatus.

The foregoing objects are accomplished by providing a light beamcharacteristic evaluation method comprising the steps of: providing alight beam source for emitting a light beam which scans a surfacelinearly; lighting the light beam source during a scanning periodequivalent to 1 dot during scanning; and evaluating characteristicsrequired of the light beam.

The foregoing objects are also accomplished by providing a light beamcharacteristic evaluation method comprising the steps of: providing atleast two light beam detection means spaced at a predetermined distancein a scanning direction of a surface to be scanned; emitting a lightbeam to the light beam detection means provided on a scanning start sideby lighting a light beam source which is employed to scan the surfacelinearly during a scanning period equivalent to 1 dot during scanning;emitting a light beam to the light beam detection means provided on ascanning end side by lighting the light beam source during the scanningperiod after elapse of a light-off period computed from a previouslydesigned scanning speed and the predetermined distance; and evaluatingscanning characteristics required of the light beam, based on adetection result of the light beam detection means provided on thescanning start side and a detection result of the light beam detectionmeans provided on the scanning end side.

The light beam source may be a semiconductor laser. The light beamdetection means may be area-type solid-state imaging elements. Thescanning characteristics may be evaluated by computing an offsetquantity between the position of the light beam on an imaging surface ofthe solid-state imaging element and a previously designed referenceposition.

The scanning period and the light-off period may be defined based on aclock signal generated by a clock generator.

The light beam source may be lit until the number of clock pulsesequivalent to 1 dot is counted and put out until the number of clockpulses equivalent to the light-off period is counted.

The foregoing objects are also accomplished by a light beamcharacteristic evaluation apparatus comprising: a light beam source forscanning a surface; a lighting control circuit for lighting the lightbeam source during a scanning period equivalent to 1 dot duringscanning; light beam detection means provided on the surface fordetecting a light beam emitted from the light beam source; andevaluation processing means for evaluating characteristics required ofthe light beam on the basis of a detection result of the beam detectionmeans.

The light beam source may be assembled into a write unit equipped withan optical scanning system. The light beam detection means may be anarea-type solid-state imaging element, and the evaluation processingmeans may compute a writing position as a characteristic required of thelight beam on the basis of a detection result of the area-typesolid-state imaging element.

The area-type solid-state imaging element may be provided with at leasttwo area-type solid-state imaging elements spaced at a predetermineddistance in a horizontal scanning direction. Computation means may beprovided for computing a light-off period from a previously designedscanning speed and the predetermined distance. After the light beam hasbeen emitted on the light beam detection means provided on a scanningstart side, the light beam source may be put out during the light-offperiod, and the light beam source may be lit again during the scanningperiod equivalent to 1 dot after elapse of the light-off period, wherebythe light beam may be emitted on the light beam detection means providedon a scanning end side, and based on detection results of the light beamdetection means, scanning characteristics required of the light beam maybe evaluated.

The foregoing objects are also accomplished by providing a light beamcharacteristic evaluation apparatus comprising: a laser light sourceprovided in a write unit having an optical scanning system, the laserlight source being employed for scanning a surface; a lighting controlcircuit for lighting the laser light source during a scanning periodequivalent to 1 dot during scanning; an area-type solid-state imagingelement provided on the surface for detecting a light beam emitted fromthe laser light source; and evaluation processing means for evaluating awriting position as a characteristic required of the light beam on thebasis of a detection result of the area-type solid-state imagingelement.

The area-type solid-state imaging element may be provided with at leasttwo area-type solid-state imaging elements spaced at a previouslydesigned predetermined distance in a horizontal scanning direction. Thelaser light source may be put out after it has been lit during ascanning period equivalent to 1 dot toward the area-type solid-stateimaging element provided on the scanning start side, and the laser lightsource may be lit again during the scanning period after elapse of alight-off period computed from a previously designed scanning speed andthe predetermined distance. The evaluation processing means may computea magnification error, by comparing a distance between a writingposition detected by the area-type solid-state imaging element on thescanning start side and a writing position detected by the area-typesolid-state imaging element on the scanning end side with thepredetermined distance.

The area-type solid-state imaging element may be provided with threearea-type solid-state imaging elements spaced in a horizontal scanningdirection, one of the three area-type solid-state imaging elements beingprovided at a center position, one of the remaining area-typesolid-state imaging elements being provided on a scanning start side,the other being provided on a scanning end side, and the area-typesolid-state imaging element at the center position being provided atequal distances from the opposite two area-type solid-state imagingelements. The laser light source may be put out after it has been litduring a scanning period equivalent to 1 dot toward the area-typesolid-state imaging element provided on the scanning start side, and thelaser light source may be lit again during the scanning period towardthe remaining area-type solid-state imaging elements after elapse of alight-off period computed from a previously designed scanning speed andthe predetermined distance. The evaluation processing means may evaluateright-left image balance as the scanning characteristics, by comparing adistance between a writing position detected by the area-typesolid-state imaging element provided on the scanning start side and awriting position detected by the middle area-type solid-state imagingelement with a distance between a writing position detected by themiddle area-type solid-state imaging element and a writing positiondetected by the area-type solid-state imaging element provided on thescanning end side.

The aforementioned light beam characteristic evaluation apparatus mayfurther comprise a clock pulse generator for defining both the scanningperiod equivalent to 1 dot and the light-off period. The light beamsource may be lit until the number of clock pulses equivalent to 1 dotis counted and put out until the number of clock pulses equivalent tothe light-off period is counted.

The aforementioned light beam characteristic evaluation apparatus mayfurther comprise computation means for computing the light-off periodfrom a previously designed scanning speed and the distance.

The write unit may be provided with synchronous sensors for determininga write timing period on the scanning start and scanning end sides inthe horizontal scanning direction. The laser light source may be litcontinuously until a light beam is detected by the synchronous sensor onthe scanning start side, and it may be put out once for 1-dot lightingafter the light beam has been detected by the synchronous sensor presenton the scanning start side.

The laser light source may be provided with two laser light sources andwherein writing to the surface to be scanned is possible by two lightbeams.

The evaluation processing means may compute a beam-to-beam pitch, basedon both a position at which the area-type solid-state imaging elementreceived a light beam emitted from one of the two laser light sourcesand a position at which the area-type solid-state imaging elementreceived a light beam emitted from the other of the two laser lightsources, and the evaluation processing means may evaluate the degree ofparallelization between two light beams by computing the beam-to-beampitch at least two or more points spaced in the horizontal scanningdirection.

The evaluation processing means may compute beam centers of thearea-type solid-state imaging elements in a vertical scanning direction(i.e., sub-scanning direction), and may evaluate a scanning linecurvature of the light beam, based on the computed beam centers.

The write unit may be equipped with a synchronous sensor for determininga write timing period on a scanning start side. The area-typesolid-state imaging element may be movable in a horizontal scanningdirection, and the lighting control circuit may be controlled so as tolight the laser light source for a period of 1 dot after a light-offperiod, related to a distance between the synchronous sensor and thearea-type solid-state imaging element, has elapsed.

The light-off period may be computed from the distance and a previouslyset theoretical scanning speed.

The foregoing objects are also accomplished by providing a light beamcharacteristic evaluation apparatus comprising: a light beam source forscanning a surface; a lighting control circuit for lighting the lightbeam source during a scanning period equivalent to 1 dot duringscanning; an area-type solid-state imaging element provided on thesurface for detecting a light beam from the light beam source lit by thelighting control circuit; and evaluation processing means for computinga diameter of the light beam on the surface.

The beam diameter may be evaluated at at least two places in a scanningdirection.

The light beam may be moved linearly in a horizontal scanning direction,and the computation means may compute both a beam diameter in thehorizontal scanning direction and a beam diameter in a vertical scanningdirection perpendicular to the horizontal scanning direction.

The evaluation processing means may compute a center position of thelight beam from both the beam diameter in the horizontal scanningdirection and the beam diameter in the vertical scanning direction.

The evaluation processing means may compute a beam shape present on thesurface from both the beam diameter in the horizontal scanning directionand the beam diameter in the vertical scanning direction.

The evaluation processing means may compute a center position of thelight beam, by computing both an intensity distribution of the beamdiameter in the horizontal scanning direction and an intensitydistribution of the beam diameter in the vertical scanning direction oneach pixel of the area-type solid-state imaging element.

The foregoing objects are also accomplished by providing a light beamcharacteristic evaluation apparatus for evaluating a beam diameter on afirst surface scanned by a light beam emitted from a laser light sourcewhich is provided in a write unit having an optical scanning system andalso which is employed to perform only writing on a latent imagecarrier, the light beam characteristic evaluation apparatus comprising:a lighting control circuit for lighting the laser light source during ascanning period equivalent to 1 dot during scanning; an area-typesolid-state imaging element provided on a second surface equivalent tothe first surface for detecting a light beam from the laser light sourcelit by the lighting control circuit; and evaluation processing means forcomputing a diameter of the light beam on the second equivalent surface.

The light beam may be moved linearly in a horizontal scanning direction,and the computation means may compute both a beam diameter in thehorizontal scanning direction and a be am diameter in a verticalscanning direction perpendicular to the horizontal scanning direction.

The evaluation processing means may compute a c enter position of thelight beam from both the beam diameter in the horizontal scanningdirection and the beam diameter in the vertical scanning direction.

The write unit may be equipped with a synchronous sensor for determininga write timing period of the latent image carrier, and the opticalscanning system may be equipped with an f θ lens. The area-typesolid-state imaging element may be arranged at an image height positionequivalent to an optical axis position on the second equivalent surface,and the lighting control circuit may be controlled so as to light thelaser light source for a period of 1 dot after a light-off period,related to a distance between the synchronous sensor and the area-typesolid-state imaging element, has elapsed.

The evaluation processing means may evaluate a writing position, amagnification error, image balance, a scanning line curvature in ahorizontal scanning direction, and a degree of parallelization of alight beam, based on the center position of the light beam.

The foregoing objects are also accomplished by providing a light beamcharacteristic evaluation method comprising the steps of: providing alight beam source for emitting a light beam which scans a surfacelinearly; lighting the light beam source during a scanning periodequivalent to 1 dot during scanning; and computing a diameter or shapeof the light beam.

The foregoing objects are also accomplished by providing an adjustmentmethod comprising the steps of: providing a write unit incorporating anoptical scanning system to form an electrostatic latent image on asurface of a latent image carrier by a light beam emitted from a laserlight source; and moving the write unit relatively in a horizontalscanning direction against the latent image carrier in correspondence toan offset quantity of the light beam in the horizontal scanningdirection, thereby adjusting the write unit.

The foregoing objects are also accomplished by providing an adjustmentmethod comprising the steps of: providing a write unit incorporating anoptical scanning system to form an electrostatic latent image on asurface of a latent image carrier by a light beam emitted from a laserlight source; and moving the write unit relatively in a horizontalscanning direction against an image forming unit incorporating at leastthe latent image carrier in correspondence to an offset quantity of thelight beam in the horizontal scanning direction, thereby adjusting thewrite unit.

The foregoing objects are also accomplished by an adjustment apparatuscomprising: a write unit incorporating an optical scanning system toform an electrostatic latent image on a surface of a latent imagecarrier by a light beam emitted from a laser light source; an imageforming unit incorporating at least the latent image carrier; and movingmeans for moving the write unit and the image forming unit relativelyalong a horizontal scanning direction in order to adjust an offsetquantity of the light beam in the horizontal scanning direction.

The image forming unit may be provided with a developing unit.

The moving means may be constituted by a guide hole formed in a mainbody constitution wall of an image forming device and extendinglengthwise in the horizontal scanning direction, and a support pinformed in either the write unit or the image forming unit and fittedinto the guide hole.

The moving means may be constituted by an adjusting screw for movingeither the write unit or the image forming unit in the horizontalscanning direction, and elastic means for urging either the write unitor image forming unit moved by the adjusting screw so that a point endof the adjusting screw abuts on the unit.

The moving means may be constituted by an adjusting screw for movingeither the write unit or the image forming unit in the horizontalscanning direction and a boss portion provided in either the write unitor image forming unit moved by the adjusting screw, the adjusting screwmeshing with the boss portion.

The foregoing objects are also accomplished by an adjustment methodwherein a write unit, incorporating an optical scanning system to forman electrostatic latent image on a surface of a latent image carrier bya light beam emitted from a laser light source, is adjusted by movingthe write unit relatively in a vertical scanning direction against thelatent image carrier in correspondence to an offset quantity of thelight beam in the vertical scanning direction, the vertical scanningdirection being defined as a direction perpendicular to both a travelingdirection of a light beam which is incident from the write unit towardthe image forming unit and a horizontal direction.

The foregoing objects are also accomplished by an adjustment methodwherein a write unit, incorporating an optical scanning system to forman electrostatic latent image on a surface of a latent image carrier bya light beam emitted from a laser light source, is adjusted by movingthe write unit relatively in a vertical scanning direction against animage forming unit incorporating at least the latent image carrier incorrespondence to an offset quantity of the light beam in the verticalscanning direction, the vertical scanning direction being defined as adirection perpendicular to both a traveling direction of a light beamwhich is incident from the write unit toward the image forming unit anda horizontal direction.

The foregoing objects are also accomplished by an adjustment apparatuscomprising: a write unit incorporating an optical scanning system toform an electrostatic latent image on a surface of a latent imagecarrier by a light beam emitted from a laser light source; an imageforming unit incorporating at least the latent image carrier; and movingmeans for moving the write unit and the image forming unit relativelyalong a vertical scanning direction defined as a direction perpendicularto both a traveling direction of a light beam which is incident from thewrite unit toward the image forming unit and a horizontal direction inorder to adjust an offset quantity of the light beam in the verticalscanning direction.

The image forming unit may be provided with a developing unit.

The moving means may be constituted by a guide hole formed in a mainbody constitution wall of an image forming device and extendinglengthwise in the vertical scanning direction, and a support pin formedin either the write unit or the image forming unit and fitted into theguide hole.

The moving means may be constituted by an adjusting screw for movingeither the write unit or the image forming unit in the vertical scanningdirection and elastic means provided in either the write unit or imageforming unit moved by the adjusting screw, the elastic means being usedfor urging the moved unit so that a point end of the adjusting screwabuts on the unit.

The moving means may be constituted by an adjusting screw for movingeither the write unit or the image forming unit in the vertical scanningdirection and a boss portion provided in either the write unit or imageforming unit moved by the adjusting screw, the adjusting screw meshingwith the boss portion.

The foregoing objects are also accomplished by an adjustment methodcomprising the steps of: providing a write unit which incorporates bothan optical scanning system and a synchronous sensor for determining awrite timing period with respect to a latent image carrier in order toform an electrostatic latent image on a surface of the latent imagecarrier by a light beam emitted from a laser light source; and movingthe synchronous sensor in a horizontal direction in correspondence to anoffset quantity of the light beam of the write unit with respect to thelatent image carrier in the horizontal scanning direction, therebyadjusting the offset quantity.

The foregoing objects are also accomplished by an adjustment apparatuscomprising: a write unit incorporating both an optical scanning systemand a synchronous sensor for determining a write timing period withrespect to a latent image carrier in order to form an electrostaticlatent image on a surface of the latent image carrier by a light beamemitted from a laser light source; and moving means for moving thesynchronous sensor in a horizontal scanning direction in order to adjustan offset quantity of the light beam of the write unit with respect tothe latent image carrier in the horizontal scanning direction.

The moving means may be constituted by a movable body for holding thesynchronous sensor, a guide shaft for guiding the movable body in thehorizontal scanning direction, an adjusting screw for moving the movablebody by its point end portion abutting on the movable body, and meansfor urging the movable body in a direction which abuts on the point endportion of the adjusting screw.

The foregoing objects are also accomplished by a light beamcharacteristic evaluation method comprising the steps of: lighting alaser light source of a light beam which is employed to scan a surfacelinearly during a scanning period equivalent to 1 dot; moving anarea-type solid-state imaging element which detects the light beam inorder along a traveling direction of the light beam with the surface asa reference position; and obtaining a beam image at each position by thearea-type solid-state imaging element.

Based on each beam image obtained by the area-type solid-state imagingelement at each position in the traveling direction of the light beam, abeam diameter may be computed at the each position of the light beam,whereby a beam diameter with respect to a depth direction may beevaluated.

From the beam diameter and a depth, a depth curve representative of arelation of the beam diameter to the depth is computed, a beam waistposition may be specified based on the depth curve, and from adifference between the beam waist position and the reference position, abeam waist position correction quantity may be computed.

The foregoing objects are also accomplished by a light beamcharacteristic evaluation apparatus comprising: a light beam source foremitting a light beam which scans a surface linearly; a 1-dot lightingcontrol circuit for lighting the light beam source during a scanningperiod equivalent to 1 dot; an area-type solid-state imaging element fordetecting the light beam, the element being movable in a travelingdirection of the light beam with the surface as a reference position;and evaluation processing means for computing a beam diameter at eachposition in the traveling direction of the light beam, based on thelight beam detected by the area-type solid-state imaging element.

The evaluation processing means may compute a depth curve representativeof a relation of the beam diameter to a depth from the beam diameter anddepth and specify a beam waist position on the basis of the depth curve.Furthermore, the evaluation processing means may compute a beam waistposition correction quantity from a difference between the beam waistposition and the reference position.

The foregoing objects are also accomplished by a light beamcharacteristic evaluation apparatus comprising: a write unit with anoptical scanning system; a light beam source for emitting a light beamwhich scans a surface linearly, the light beam source being provided inthe write unit; a 1-dot lighting control circuit for lighting the lightbeam source during a scanning period equivalent to 1 dot; an area-typesolid-state imaging element for detecting the light beam, the elementbeing movable in a traveling direction of the light beam with thesurface as a reference position; and evaluation processing means forcomputing a beam diameter at each position in the traveling direction ofthe light beam, based on the light beam detected by the area-typesolid-state imaging element; the write unit being equipped with asynchronous sensor for determining a write timing period on a scanningstart side in a horizontal scanning direction; the laser light sourcebeing lit continuously until the light beam is detected by thesynchronous sensor present on a scanning start side and also being putout once for 1-dot lighting after the light beam has been detected bythe synchronous sensor present on the scanning start side; and the 1-dotlighting control circuit being controlled so that the laser light sourceis lit after elapse of the write timing period.

The aforementioned light beam characteristic evaluation apparatus mayfurther comprise: computation means for computing the write timingperiod from both a distance in a horizontal direction between thesynchronous sensor and the area-type solid-state imaging element and apreviously designed scanning speed; and a clock pulse generator fordefining both the scanning period equivalent to 1 dot and the writetiming period. The light beam source is lit until a light beam isdetected by the synchronous sensor, is put out until the number of clockpulses equivalent to the write timing period is counted since thesynchronous sensor detected the light beam, and is lit by the 1-dotlighting control circuit until the number of clock pulses equivalent to1 dot is counted.

The foregoing objects are also accomplished by an adjustment methodwherein at least either an image forming unit or a write unit is movedso that a space therebetween is increased or decreased, in order toadjust an optical path length between a laser light source and a writingobject surface of the image forming unit and based on a beam waistposition correction quantity obtained by a light beam characteristicevaluation method comprising the steps of: (a) lighting the laser lightsource of a light beam which is employed to scan the writing objectsurface of the image forming unit linearly during a scanning periodequivalent to 1 dot; (b) moving an area-type solid-state imaging elementwhich detects the light beam in order along a traveling direction of thelight beam with the writing object surface as a reference position,thereby obtaining a beam image at each position by the area-typesolid-state imaging element; (c) based on each beam image obtained bythe area-type solid-state imaging element at each position in atraveling direction of the light beam, computing a beam diameter at theeach position of the light beam and thereby computing a beam diameterwith respect to a depth direction; (d) from the beam diameter and adepth, computing a depth curve representative of a relation of the beamdiameter to the depth; (e) specifying a beam waist position on the basisof the depth curve; and (f) from a difference between the beam waistposition and the reference position, computing the beam waist positioncorrection quantity.

The foregoing objects are also accomplished by an adjustment apparatuswhich comprises optical path length adjustment means for moving at leasteither an image forming unit or a write unit so that a spacetherebetween is increased or decreased, in order to adjust an opticalpath length between a laser light source and a writing object surface ofthe image forming unit and based on a beam waist position correctionquantity obtained by a light beam characteristic evaluation methodcomprising the steps of: (a) lighting the laser light source of a lightbeam which is employed to scan the writing object surface of the imageforming unit linearly during a scanning period equivalent to 1 dot; (b)moving an area-type solid-state imaging element which detects the lightbeam in order along a traveling direction of the light beam with thewriting object surface as a reference position, thereby obtaining a beamimage at each position by the area-type solid-state imaging element; (c)based on each beam image obtained by the area-type solid-state imagingelement at each position in a traveling direction of the light beam,computing a beam diameter at the each position of the light beam andthereby computing a beam diameter with respect to a depth direction; (d)from the beam diameter and a depth, computing a depth curverepresentative of a relation of the beam diameter to the depth; (e)specifying a beam waist position on the basis of the depth curve; and(f) from a difference between the beam waist position and the referenceposition, computing the beam waist position correction quantity.

In order to change an optical path length between a surface of a latentimage carrier of the image forming unit and the write unit, the opticalpath length adjustment means may be constituted by a guide hole formedin a main body constitution wall of an image forming device and a guidepin formed in either the write unit or the image forming unit and fittedinto the guide hole.

The foregoing objects are also accomplished by an adjustment methodwherein an optical path length between a laser light source and asurface to be scanned is adjusted based on a beam waist positioncorrection quantity obtained by a light beam characteristic evaluationmethod comprising the steps of: (a) lighting the laser light source of alight beam which is employed to scan the surface linearly during ascanning period equivalent to 1 dot; (b) moving an area-type solid-stateimaging element which detects the light beam in order along a travelingdirection of the light beam with the writing object surface as areference position, thereby obtaining a beam image at each position bythe area-type solid-state imaging element; (c) based on each beam imageobtained by the area-type solid-state imaging element at each positionin a traveling direction of the light beam, computing a beam diameter atthe each position of the light beam and thereby computing a beamdiameter with respect to a depth direction; (d) from the beam diameterand a depth, computing a depth curve representative of a relation of thebeam diameter to the depth; (e) specifying a beam waist position on thebasis of the depth curve; and (f) from a difference between the beamwaist position and the reference position, computing the beam waistposition correction quantity.

The foregoing objects are also accomplished by an adjustment apparatuswhich comprises optical path length adjustment means for adjusting anoptical path length between a laser light source and a surface to bescanned, based on a beam waist position correction quantity obtained bya light beam characteristic evaluation method comprising the steps of:(a) lighting the laser light source of a light beam which is employed toscan the surface linearly during a scanning period equivalent to 1 dot;(b) moving an area-type solid-state imaging element which detects thelight beam in order along a traveling direction of the light beam withthe writing object surface as a reference position, thereby obtaining abeam image at each position by the area-type solid-state imagingelement; (c) based on each beam image obtained by the area-typesolid-state imaging element at each position in a traveling direction ofthe light beam, computing a beam diameter at the each position of thelight beam and thereby computing a beam diameter with respect to a depthdirection; (d) from the beam diameter and a depth, computing a depthcurve representative of a relation of the beam diameter to the depth;(e) specifying a beam waist position on the basis of the depth curve;and (f) from a difference between the beam waist position and thereference position, computing the beam waist position correctionquantity.

The laser light source may be equipped with a semiconductor laser foremitting a light beam, a collimator lens for collimating the light beam,and a lens barrel for holding the collimator lens. The lens barrel maybe formed with a first screw portion along an optical axis direction.The constitution wall of the write unit may be formed with a secondscrew portion at a position at which the lens barrel is arranged, thefirst screw portion meshing with the second screw portion. The opticalpath length adjustment means may be constituted by the first and secondscrew portions.

The foregoing objects are also accomplished by a light beamcharacteristic evaluation apparatus which is employed in a method ofevaluating characteristics required of a light beam by forming the lightbeam on an area-type imaging element installed on a first surfaceequivalent to a second surface to be scanned, the light beam beingemitted from a laser light source which is employed to scan the secondsurface linearly, the light beam characteristic evaluation apparatuscomprising: a reference laser light source for determining previouslydesigned reference positions of the light beam present on the secondsurface in horizontal and vertical scanning directions; a holder memberfor holding the reference laser light source; an angular positiondetermination member for holding the holder member so that the holdermember is rotatable and determining a rotational angular position of thereference laser light source; and a positioning reference base forpositioning the angular position determination member so that a centerof rotation of the holder member is aligned with a previously designedemission line of the light beam; wherein a reference pixel equivalent tothe reference position on the area-type imaging element is specified, byrotating the holder member on the center of rotation and receiving areference light beam emitted from the reference laser light source at atleast two rotational angular positions with the area-type imagingelement.

The positioning reference base may extend in the horizontal scanningdirection.

The reference laser light source may be a semiconductor laser.

The laser light source may be provided in a write unit incorporating anoptical scanning system.

The evaluation may be performed by lighting the laser light sourceduring a scanning period equivalent to 1 dot during scanning.

The foregoing objects are also accomplished by a light beamcharacteristic evaluation apparatus which is employed in a method ofevaluating characteristics required of a light beam by forming the lightbeam on an area-type imaging element installed on a first surfaceequivalent to a second surface to be scanned, the light beam beingemitted from a laser light source provided in a write unit having anoptical scanning system for linearly scanning the second surface of alatent image carrier provided in an image forming unit, the light beamcharacteristic evaluation apparatus comprising: a positioning member forpositioning the write unit with respect to the image forming unit; areference laser light source for determining previously designedreference positions of a light beam on the second surface in horizontaland vertical scanning directions, the light beam being emitted from thelaser light source; a holder member for holding the reference laserlight source; an angular position determination member for holding theholder member so that the holder member is rotatable and determining arotational angular position of the reference laser light source; and apositioning reference base for positioning the angular positiondetermination member so that a center of rotation of the holder memberis aligned with a previously designed emission line of the light beamemitted from the write unit, the positioning reference base beingprovided in a positioning base; wherein a reference pixel equivalent tothe reference position on the area-type imaging element is specified, byrotating the holder member on the center of rotation and receiving areference light beam emitted from the reference laser light source at atleast two rotational angular positions with the area-type imagingelement.

The rotational angular positions may be symmetrical positions spaced 180degrees.

The angular position determination member may be provided on thepositioning reference base so that it can be relocated in the horizontalscanning direction.

The aforementioned light beam characteristic evaluation apparatus mayfurther comprise adjustment means for adjusting an imaging surface ofthe area-type imaging element so that the imaging surface is located atthe first surface.

The foregoing objects are also accomplished by a light beamcharacteristic evaluation apparatus which is employed in an evaluationmethod comprising the steps of: lighting a laser light source during ascanning period equivalent to 1 dot during scanning, the laser lightsource being provided in a write unit having an optical scanning systemfor linearly scanning a first surface of a latent image carrier of animage forming unit; forming the light beam on at least two or morearea-type imaging elements spaced in a horizontal scanning direction andprovided on a second surface equivalent to the first surface to bescanned; and evaluating characteristics required of the light beam; thelight beam characteristic evaluation apparatus comprising: a positioningmember for positioning the write unit with respect to the image formingunit; a reference laser light source for determining previously designedreference positions of a light beam on the first surface in horizontaland vertical scanning directions, the light beam being emitted from thelaser light source; a cylindrical holder member for holding thereference laser light source; angular position determination members fordetermining a rotational angular position of the reference laser lightsource, the determination members having a circular fitting hole intowhich the cylindrical holder member is rotatably fitted; and apositioning reference base for positioning the angular positiondetermination members so that a center of rotation of the cylindricalholder member is aligned with a previously designed emission line of thelight beam emitted from the write unit, the positioning reference basebeing provided in a positioning base; wherein a reference pixelequivalent to the reference position on the area-type imaging element isspecified, by rotating the cylindrical holder member and receiving areference light beam emitted from the reference laser light source at atleast two rotational angular positions with the area-type imagingelements.

The angular position determination member may be provided with anengagement pin and the cylindrical holder member is provided with anengagement hole which engages with the engagement pin.

The rotational angular positions may be symmetrical positions spaced 180degrees.

The angular position determination member may be provided in thepositioning reference base so that it can be relocated in the horizontalscanning direction.

The angular position determination members may be spaced in thehorizontal scanning direction and provided in correspondence to thearea-type imaging elements.

Once a reference pixel of a certain area-type imaging element has beenspecified by rotating the cylindrical holder member, the specificationof reference pixels of the remaining area-type imaging elements isperformed without rotating the cylindrical holder member.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and advantages will become apparent from thefollowing detailed description when read in conjunction with theaccompanying drawings wherein:

FIG. 1 is an explanatory diagram showing a conventional light beamscanning characteristic evaluation apparatus;

FIG. 2 is an explanatory diagram showing the conventional light beamscanning characteristic evaluation apparatus and also showing how thediameter of a light beam is measured with a one-dimensional CCD duringscanning;

FIG. 3 is an explanatory diagram when the diameter of the light beam ismeasured during scanning with the one-dimensional CCD shown in FIG. 2 onthe assumption that the light beam shown in FIG. 2 is stationary;

FIG. 4 is a perspective view showing the interior constitution of awrite unit according to the present invention;

FIG. 5 is a diagram for explaining the principles of a light beamcharacteristic evaluation apparatus according to a first embodiment ofthe present invention, three CCD cameras being spaced in a horizontalscanning direction;

FIG. 6 is a conceptual diagram showing the area-type imaging element ofthe CCD camera shown in FIG. 5;

FIG. 7 is a diagram for explaining a previously set theoretical idealimage (beam spot) which should be described on a scanned surface by thewrite unit shown in FIG. 4;

FIG. 8 is an explanatory diagram for explaining the 1-dot control timingof the light beam shown in FIG. 5;

FIG. 9 is a diagram showing beam spots formed on the area-type imagingelements of the CCD cameras shown in FIG. 5;

FIG. 10 is a diagram for explaining the evaluation apparatus accordingto a second embodiment of the present invention, two CCD cameras beingspaced in the horizontal scanning direction;

FIG. 11 is an explanatory diagram for explaining the 1-dot controltiming of the light beam shown in FIG. 10;

FIG. 12 is a diagram for explaining the evaluation apparatus accordingto a third embodiment of the present invention, a single CCD camerabeing provided at a center position in the horizontal scanningdirection;

FIG. 13 is an explanatory diagram for explaining the 1-dot controltiming of the light beam shown in FIG. 12;

FIG. 14 is an explanatory diagram of the beam spot (laser spot) formedon the area-type imaging element of the CCD camera shown in FIG. 12;

FIG. 15 is an explanatory diagram used to explain how a light beamintensity distribution curve is obtained based on the beam spot shown inFIG. 14;

FIG. 16 is a light beam intensity distribution curve diagram used toexplain how the center position of a light beam is computed based on thelight beam intensity distribution curve shown in FIG. 15 by anevaluation processing circuit;

FIG. 17 is a diagram for explaining the evaluation apparatus accordingto a fourth embodiment of the present invention, a single CCD camerabeing constituted so that it is moved in both the horizontal scanningdirection and the vertical scanning direction;

FIG. 18 is a flowchart showing an example of the process performed bythe light beam characteristic evaluation apparatus shown in FIG. 17;

FIGS 19(a) through 19(j) are each an explanatory diagram for explainingan example of the characteristics which are evaluated by the light beamcharacteristic evaluation apparatus according to the present invention;

FIG. 19(a) is a diagram showing the offset of writing positions in thehorizontal scanning direction;

FIG. 19(b) is a diagram showing the offset of writing positions in thevertical scanning direction;

FIG. 19(c) is a diagram used to explain pitch fluctuation present on thesurfaces of a polygon mirror in the horizontal scanning direction;

FIG. 19(d) is a diagram used to explain pitch fluctuation present on thesurfaces of the polygon mirror in the vertical scanning direction;

FIG. 19(e) is a diagram used to explain a magnification error;

FIG. 19(f) is a diagram used to explain the inclined angle of a scanningline;

FIG. 19(g) is a diagram used to explain magnification error deviation;

FIG. 19(h) is a diagram used to explain a scanning line curvature;

FIG. 19(i) is a diagram used to explain a depth curve;

FIG. 19(j) is a diagram used to explain a beam-to-beam pitch;

FIG. 20 is a diagram used to explain a structure for adjusting writingpositions in the horizontal direction and is an explanatory diagramshowing a state in which the center of a light beam is offset from areference position present on a writing start side;

FIG. 21 is a partially sectional view showing an example of the writingposition adjustment means for adjusting the horizontal scanning offsetof the beam center from the reference position present on the writingstart side shown in FIG. 20 and is a partially sectional conceptual viewshowing the positional adjustment structure of a synchronous sensor;

FIG. 22 is a diagram for explaining the writing adjustment timing thatis performed by the synchronous sensor;

FIG. 23 is an explanatory diagram of structure 1 for adjusting a writingposition in a horizontal scanning direction by moving a write unit or animage forming unit, showing the relative positional relation between thewrite unit and the image forming unit;

FIG. 24 is a partially sectional conceptual view showing an adjustmentstructure which adjusts writing start timing by moving the image formingunit relatively against the write unit shown in FIG. 23 in thehorizontal scanning direction;

FIG. 25 is an explanatory diagram of structure 2 for adjusting a writingposition in the horizontal scanning direction by moving the write unitor the image forming unit, and is a partially sectional conceptual viewshowing an adjustment structure which adjusts writing start timing bymoving the image forming unit relatively against the write unit shown inFIG. 23 in the horizontal scanning direction;

FIG. 26 is an explanatory diagram of structure 3 for adjusting a writingposition in the horizontal scanning direction by moving the write unitor the image forming unit, and is a partially sectional conceptual viewshowing an adjustment structure which adjusts writing start timing bymoving the image forming unit relatively against the write unit shown inFIG. 23 in the horizontal scanning direction;

FIG. 27 is an explanatory diagram of structure 4 for adjusting a writingposition in the horizontal scanning direction by moving the write unitor the image forming unit, and is a partially sectional conceptual viewshowing an adjustment structure which adjusts writing start timing bymoving the image forming unit relatively against the write unit shown inFIG. 23 in the horizontal scanning direction;

FIG. 28 is an explanatory diagram of structure 5 for adjusting a writingposition in the horizontal scanning direction by moving the write unitor the image forming unit, and is a partially sectional conceptual viewshowing an adjustment structure which adjusts writing start timing bymoving the image forming unit relatively against the write unit shown inFIG. 23 in the horizontal scanning direction;

FIG. 29 is an explanatory diagram of structure for adjusting a writingposition in a vertical scanning direction by moving the write unit orthe image forming unit, and is an explanatory diagram showing the statein which the center of a light beam is offset from a reference positionpresent on a writing start side in the vertical scanning direction;

FIG. 30 is an explanatory diagram of structure for adjusting a writingposition in the vertical scanning direction by moving the write unit orthe image forming unit, and is a partially sectional conceptual viewshowing an adjustment structure which adjusts writing start timing bymoving the image forming unit relatively against the write unit shown inFIG. 23 in the vertical scanning direction;

FIG. 31(a) is an explanatory diagram used in a light beam characteristicevaluation apparatus of a fourth embodiment of the present invention andis an explanatory diagram of the light beam characteristic evaluationapparatus which evaluates the depth curve of a light beam by moving aCCD camera in the horizontal scanning and vertical scanning directions;

FIG. 31(b) is a diagram showing an example of the depth curve obtainedby the beam characteristic evaluation apparatus shown in FIG. 31(a);

FIG. 32 is an explanatory diagram of an adjustment structure whichadjusts a depth by means of a laser diode unit, and is a partiallysectional view showing an optical path length adjustment structure whichadjusts an optical path length by adjusting the position of a collimatorlens in an optical axis direction, based on the depth curve obtained bythe light beam characteristic evaluation apparatus shown in the fourthembodiment of the present invention;

FIG. 33 is an explanatory diagram of structure 1 for adjusting a depthby means of a write unit or an image forming unit, and is a partiallysectional view showing an optical path length adjustment structure whichadjusts an optical path length by adjusting the gap between the writeunit and the image forming unit, based on the depth curve obtained bythe light beam characteristic evaluation apparatus shown in the fourthembodiment of the present invention;

FIG. 34 is an explanatory diagram of structure 2 for adjusting a depthby means of the write unit or the image forming unit, and is a partiallysectional view showing an optical path length adjustment structure whichadjusts an optical path length by adjusting the gap between the writeunit and the image forming unit, based on the depth curve obtained bythe light beam characteristic evaluation apparatus shown in the fourthembodiment of the present invention;

FIG. 35 shows a detailed structure of the evaluation apparatuses 1-4,and is a side view showing the mounted state of the write unit onto animage forming device;

FIG 36 is a plan view showing the mounted state of the write unit ontothe image forming device;

FIG. 37 is a diagram showing the exterior configuration of the writeunit shown in FIGS. 35 and 36;

FIG. 38 is a front view showing the mounted state of the write unit ontothe image forming device;

FIG. 39 is a partially enlarged plan view showing the layout relationbetween a positioning reference base and CCD cameras attached to areference base attaching portion;

FIG. 40(a) is a plan view of the positioning reference base shown inFIG. 39;

FIG. 40(b) is a view taken in a direction of arrow c1 in FIG. 40(a);

FIG. 40(c) is a view taken in a direction of arrow c2 in FIG. 40(b);

FIG. 40(d) is a view taken in a direction of arrow c3 in FIG. 40(b);

FIG. 41 is a partially enlarged plan view showing the layout relationbetween the positioning reference base and CCD cameras attached to thereference base attaching portion;

FIG 42(a) is a plan view of the positioning block member shown in FIGS.39 and 41;

FIG. 42(b) is a view taken in a direction of arrow c4 in FIG. 42(a);

FIG. 42(c) is a view taken in a direction of arrow c5 in FIG. 42(a);

FIG. 42(d) is a view taken in a direction of arrow c6 in FIG. 40(c);

FIG. 43(a) is a side view of the LD holder plate shown in FIG. 41;

FIG. 43(b) is a view taken in a direction of arrow c7 in FIG. 43(a);

FIG. 44 is a diagram used to explain how a reference pixel of anarea-type CCD camera unit is specified by a reference laser lightsource;

FIG. 45(a) is a partially enlarged view showing the LD holder plate andthe positioning block member and also showing the state before the LDholder plate is rotated 180 degrees;

FIG. 45(b) is a partially enlarged view showing the LD holder plate andthe positioning block member and also showing the state after the LDholder plate has been rotated 180 degrees;

FIG. 46 is a plan view showing the mounted state of a write unit onto animage forming device;

FIG. 47 is a side view showing the mounted state of the write unit ontothe image forming device and also showing the state before the writeunit is clamped;

FIG. 48 is a front view showing the mounted state of the write unit andalso showing the state before the write unit is clamped;

FIG. 49 is a plan view showing the positional relation between the CCDcamera unit and the reference laser diode attached to the support baseshown in FIG. 47;

FIG. 50 is a plan view showing the positioning reference base and thepositioning block attached to the write unit;

FIG 51 is an enlarged side view of the positioning block shown in FIG.49;

FIG. 52(a) is an explanatory diagram of a structure for adjusting awriting position in the horizontal scanning direction by moving a sheetloading position, and is a schematic view of the inner construction ofan image forming unit;

FIG. 52(b) shows an arrangement of LEDs shown in FIG. 52(a);

FIG. 52(c) shows a side guide attached to a sheet loading tray;

FIG. 53(a) is a diagram showing how a reflecting mirror or an fθ lens isadjusted with respect to the optical axis when there is only amagnification error; and

FIG. 53(b) is a diagram showing how the reflecting mirror or the fθ lensis adjusted with respect to the optical axis when there is only scanningline tilt.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will hereinafter be described indetail in reference to the drawings.

FIG. 4 shows a perspective view of an example of the positional relationbetween a write unit with a light beam source (laser light source) and aphotosensitive drum. The light beam source is an object of evaluationwhich is evaluated by a light beam characteristic evaluation methodaccording to the present invention. The photosensitive drum is a latentimage carrier to which a beam of light emitted from the write unit iswritten.

In FIG. 4, reference numerals 11 and 12 denote laser diodes(semiconductor lasers), 13 and 14 denote collimator lenses. Referencenumeral 15 denotes an optical member for synthesizing optical paths, 16a quarter-wave plate, and 17 and 18 beam shaping systems. These opticalelements 11 through 18 constitute a laser light source section (lightbeam source) Sou. Two light beams P1 emitted from the laser light sourcesection Sou are collimated by the collimator lenses 13 and 14 and areguided to a polygon mirror 19 constituting part of an optical scanningsystem. The light beams P1 are reflected and deflected in a horizontalscanning direction (i.e., main scanning direction) Q1 by the surfaces 20a to 20 f of the polygon mirror 19.

The reflected and deflected light beams are guided to reflecting mirrors21 and 22 constituting part of an optical fθ system 23. The light beamsreflected and deflected by the reflecting mirror 22 are passed throughthe optical fθ system 23 and are guided to an inclined reflecting mirror24. The inclined reflecting mirror 24 guides the light beams to thesurface 26 of a photosensitive drum 25 serving as a latent image carrier25. The surface 26 of the photosensitive drum 25 is scanned linearly inthe horizontal scanning direction Q1 by the light beams P1. This surface26 is a surface which is scanned by the light beams P1, and writing isperformed on this surface.

The laser light source section Sou, polygon mirror 19, reflectingmirrors 21 and 22, fθ lens 23, and reflecting mirror 24 are mounted inthe write unit 1. The photosensitive drum 25 is mounted in an imageforming unit (described later).

Synchronous sensors 27 and 28 are provided on the longitudinal oppositesides of the reflecting mirror 24 (in the horizontal scanning directionQ1 of the light beam) in the write unit 1. The first synchronous sensor27 is employed to determine writing start timing, while the secondsynchronous sensor 28 is employed to determine writing end timing.

The characteristics of the light beams P1 emitted from this write unit 1are an object of evaluation. In FIG. 4, although writing to the surface26 of the photosensitive drum 25 is performed with two scanning lines,the case of a single laser diode and the case of two laser diodes areessentially the same in the evaluation principle of the characteristicsof the light beam. Therefore, for the case of a single laser diode, thelight beam characteristic evaluation items according to the presentinvention will be described in reference to Table 1.

TABLE 1 Number of Characteristic evaluation items CCD cameras Case of 1beam Case of 2 beams Remarks 1 a) Writing Writing position position in ain a horizontal horizontal scanning direction scanning direction b)Writing posi- Writing position tion in a vertical in a vertical scanningdirection scanning direction c) Pitch Pitch fluctuation Positionaloffset fluctuation in in a horizontal in a horizontal a horizontalscanning direction scanning direction scanning direction at each surfaceof a polygon mirror d) Surface tilt in Surface tilt in a Positionaloffset a vertical vertical scanning in a vertical scan- scanningdirection direction ning direction at each surface of a polygon mirrore) Beam diameter Beam diameter in in a horizontal a horizontal scanningdirection scanning direction f) Beam diameter Beam diameter in in avertical a vertical scanning direction scanning direction m)Beam-to-beam Beam-to-beam pitch distance in a vertical scanningdirection between a plurality of beams 2 g) Magnification MagnificationHorizontal error error scanning component h) Scanning line Scanning lineVertical scanning tilt tilt component k) Scanning Scanning period periodl) Depth Depth 3 or more i) Magnification Magnification Horizontal errordeviation error deviation scanning component j) Scanning line Scanningline Vertical scanning curvature curvature component

As shown in Table 1, the light beam characteristic evaluation itemsinclude a) writing position in the horizontal scanning direction (i.e.,main scanning direction), b) writing position in the vertical scanningdirection (i.e., sub-scanning direction), c) pitch fluctuation in thehorizontal scanning direction, d) surface tilt in the vertical scanningdirection, e) beam diameter in the horizontal scanning direction, f)beam diameter in the vertical scanning direction, g) magnificationerror, h) scanning line tilt, i) magnification error deviation, j)scanning line curvature, k) scanning period, 1) depth, and m)beam-to-beam pitch. (A write unit which can emit a plurality of lightbeams at the same time is described in U.S. Pat. No. 96-675722. In theembodiment of the present invention, since two laser diodes (LDs) 11 and12 are arranged in the vertical scanning direction, a beam-to-beam pitchis in the vertical scanning direction.)

The evaluation items will hereinafter be described in detail.

a) Evaluation of a Writing Position in the Horizontal Scanning Direction

A light beam emitted from the LD is reflected by the polygon mirror 19.The reflected light beam is incident on the photosensitive body throughthe optical fθ lens system. The position at which writing is performedon this photosensitive body is evaluated in the horizontal direction, orthe timing is evaluated.

For instance, as shown in FIG. 19(a), assume that a predeterminedwriting position center (write timing) is “O” and also a positionwritten to an area-type imaging element (described later) is “zz.” Inthis case, the offset quantity between the writing position center O andthe writing position zz is Δx in the horizontal direction. This offsetquantity Δx is evaluated.

b) Evaluation of a Writing Position in the Vertical Scanning Direction

A light beam emitted from the LD is reflected by the polygon mirror 19.The reflected light beam is incident on the photosensitive body throughthe fθ lens optical system. The position at which writing is performedon this photosensitive body is evaluated in the vertical direction, orthe timing is evaluated.

For instance, as shown in FIG. 19(b), assume that a predeterminedwriting position center (write timing) is “O” and also a positionwritten to an area-type imaging element (described later) is “zz.” Inthis case, the offset quantity between the writing position center O andthe writing position zz is Δy in the vertical direction. This offsetquantity Δy is evaluated.

c) Evaluation of Pitch Fluctuation in the Horizontal Scanning Direction

By writing a light beam many times along the horizontal scanningdirection, a desired image is formed. The polygon mirror 19 is formedwith six mirrors, and writing is performed by reflecting a light beamwith the six mirrors. For this reason, there are cases where a positionat which a light beam is written changes depending upon an accuracy ineach mirror.

Therefore, by reflecting a light beam at the surfaces of the polygonmirror 19, fluctuations in the center positions in the horizontalscanning direction of beam spots S corresponding to the surfaces areevaluated.

For example, in the case of six mirrors (six surfaces 20 a to 20 f), alight beam is reflected by each of the surfaces 20 a to 20 f of thepolygon mirror 19 and is fetched in a CCD camera (described later).Assume that the positions of the beam light written to the area-typeimaging element of the CCD camera were the ones shown in FIG. 19(c).

Also, assume that with respect to a reference center position O, thecenter positions of the beam light reflected by the surfaces 20 a to 20f were kz1, kz2, kz3, kz3, kz4, kz5, and kz6 and that the offsetquantities in the horizontal scanning direction were Δx1, Δx2, and Δx3.

In this case, if an average value Δx of the fluctuations in thehorizontal scanning direction of the surfaces, Δx=(2Δx1+2Δx2 +2Δx3)/6.

With this, it can be evaluated how a pitch varies depending upon anaccuracy in each surface of the polygon mirror 19.

In this example, although the reference center position O is employed toevaluate fluctuations in the center positions, fluctuations in pitchesin the horizontal scanning direction may be evaluated by employing anyof the center positions of the beam spots reflected by the surfaces ofthe polygon mirror 19 as a reference position.

For instance, the center position of the first fetched beam spot S maybe employed as reference. By computing a center position between beamspots S, the center position of the beam spot S with the minimum errormay be employed as a reference position. Also, the beam spot S with thehighest coincidence rate may be employed as reference.

d) Evaluation of Surface Tilt in the Vertical Scanning Direction

By writing a light beam many times along the horizontal scanningdirection, a desired image is formed. The polygon mirror 19 is formedwith six mirrors, and writing is performed by reflecting a light beamwith the six mirrors. For this reason, there are cases where a positionat which a light beam is written changes depending upon an accuracy ineach mirror.

Therefore, by reflecting a light beam at the surfaces of the polygonmirror 19, fluctuations in the center positions in the horizontalscanning direction of beam spots S corresponding to the surfaces areevaluated.

For example, in the case of six mirrors (surfaces 20 a to 20 f), a lightbeam is reflected by each of the surfaces 20 a to 20 f of the polygonmirror 19 and is fetched in a CCD camera (described later). Assume thatthe positions of the beam light written to the area-type imaging elementof the CCD camera were the ones shown in FIG. 19(d).

Also, assume that with respect to a reference center position O, thecenter positions of the beam light reflected by the surfaces 20 a to 20f were kz1, kz2, kz3, kz3, kz4, kz5, and kz6 and that the offsetquantities in the vertical scanning direction were Δy1, Δy2, and Δy3.

In this case, if an average value Ay of the fluctuations in the verticalscanning direction of the surfaces, Δy=(2Δy1+2Δy2+2Δy3)/6.

With this, it can be evaluated how a pitch varies depending upon anaccuracy in each surface of the polygon mirror 19.

In this example, although the reference center position O is employed toevaluate fluctuations in the center positions, surface tilt in thevertical scanning direction may be evaluated by employing any of thecenter positions of the beam spots reflected by the surfaces of thepolygon mirror 19 as a reference position.

For instance, the center position of the first fetched beam spot S maybe employed as reference. By computing a center position between beamspots S, the center position of the beam spot S with the minimum errormay be employed as a reference position. Also, the beam spot S with thehighest coincidence rate may be employed as reference.

e) Evaluation of a Beam Diameter in the Horizontal Scanning Direction

The beam diameter of the light beam spot S in the horizontal scanningdirection is evaluated.

f) Evaluation of a Beam Diameter in the Vertical Scanning Direction

The beam diameter of the light beam spot S in the vertical scanningdirection is evaluated.

g) Evaluation of a Magnification Error

Whether or not the space between two beam spots S has a predeterminedspace is evaluated. That is, magnification is evaluated by whether thespace is shorter or longer than a predetermined space.

For example, as shown in FIG. 19(e), if a ratio between the distance L4and the distance L5 is computed, the magnification error can beevaluated. The distance L4 represents a distance between previouslydesigned writing reference positions Z1 and Z2 on transfer papercorresponding to two points on a manuscript in the horizontal scanningdirection Q1, while the distance L5 represents a distance between thewriting positions Z1′ and Z2′ on a scanned surface actually obtained bymeasurement.

h) Evaluation of Scanning Line Tilt

If a light beam is emitted in the horizontal scanning direction, asingle scanning line will be obtained. Whether or not this scanning lineis parallel to the horizontal scanning line is evaluated.

For example, as shown in FIG. 19(f), by a difference between the offsetquantity d0 and the offset quantity d1 and the distance L6, the inclinedangle θ of the scanning line and the total offset quantity Δd areevaluated. The offset quantity d0 represents the offset quantity in thevertical scanning direction Q3 of the writing position Z1′ obtained bymeasurement performed on the horizontal scanning start side, while theoffset quantity d1 represents the offset quantity in the verticalscanning direction Q3 of the writing position Z2′ obtained bymeasurement performed on the horizontal scanning end side.

i) Evaluation of Magnification Error Deviation

In the aforementioned item g), a magnification error is evaluated byevaluating the writing positions of two beam spots S. But in theevaluation of magnification error deviation, three or more beam spotsare fetched into area-type imaging elements and the magnificationbetween spots are compared, whereby deviation between spaces isevaluated.

For example, as shown in FIG. 19(g), if the distance L7 and the distanceL8 are computed, magnification error deviation (right-left balance) canbe evaluated. The distance L7 is a distance between the middle writingposition Zm′ and the horizontal scanning start side writing position Z1′obtained by measurement, while the distance L8 is a distance between themiddle writing position Zm′ and the horizontal scanning end side writingposition Z2′ obtained by measurement.

j) Evaluation of Scanning Line Curvature

In the aforementioned item h), whether or not a light beam has beenemitted in parallel to the horizontal scanning direction is evaluated bythe positions at which two beam spots S are written. But the evaluationof scanning line curvature is performed, by fetching 3 mor more beamspots S into area-type imaging elements and evaluating the inclinationbetween beam spots in the horizontal scanning direction.

For example, as shown in FIG. 19(h), if the offset quantity d2 in thevertical scanning direction Q3 of the writing position Z1 on the writingstart side obtained by measurement, the offset quantity d4 in thevertical scanning direction Q3 of the middle writing position Zm′obtained by measurement, and the offset quantity d3 in the verticalscanning direction Q3 of the writing position Z2′ on the writing endside obtained by measurement are computed, scanning line curvature canbe evaluated.

k) Evaluation of a Scanning Period

The scanning period by a light beam can be computed by counting theperiod between the time that a beam spot is fetched in one of two CCDcameras and the time that the beam spot is fetched in the other. Inaddition, a scanning speed can be computed by dividing the distancebetween the two CCD cameras with the scanning period.

Note that one of the two CCD cameras may be replaced with synchronoussensors (scanning start detection and scanning end detection sensors)provided in the write unit 1 for synchronous detection. The details willbe described later.

l) Evaluation of a Depth

By moving the CCD camera in a direction perpendicular to the horizontalscanning direction (i.e., in the same direction as the optical axis of alight beam emitted to the CCD camera) with a light beam locked in thehorizontal scanning direction, the beam diameter in the travelingdirection of the light beam is measured, whereby a depth at a designedposition is evaluated.

For example, if the CCD camera is moved in sequence at regular intervalsin the traveling direction of a light beam and stopped and if thediameter D of the beam spot S is computed in sequence at the stoppedpositions, a beam diameter curve (depth curve) can be obtained as shownin FIG. 19(i). Reference character Bw denotes a beam waist. In thismanner, a light beam depth can be evaluated.

m) Evaluation of a Beam-to-beam Pitch

The pitches between a plurality of light beams emitted at the same timeare evaluated.

For example, as shown in FIG. 19(i), if the center positions KK and KK′of two beam spots S received by a single area-type imaging element arecomputed and the space ΔKK in the vertical scanning direction, a pitchspace ΔKK between two light beams can be evaluated.

The light beam characteristic evaluation apparatus shown in FIG. 5 canevaluate all evaluation items a to k and m except for the evaluationitem i): evaluation of a depth.

(First Embodiment of Evaluation Apparatus)

An embodiment of an evaluation apparatus will be described withreference to FIG. 5.

In FIG. 5, reference numeral 29 denotes a pulse motor for driving thepolygon mirror and reference numeral 30 denotes a drive control circuitfor controlling drive of the pulse motor. On a surface 31 equivalent tothe surface 26 of the photosensitive drum 25, the area-type imagingelements (imaging surfaces) 32 a to 34 a of CCD cameras 32 to 34 aslight beam detection means are provided at regular intervals from thescanning start side of the light beam P1 to the scanning end side.

In more detail, the CCD cameras 32 to 34 are disposed at a lightirradiation start position (of the sheet maximum size), lightirradiation completion position, and intermediate position of alight-irradiated member (i.e., latent image carrier) upon which a lightbeam is cast which has been emitted from a write unit provided in animage forming apparatus (e.g., a copying machine). In this way, aposition to be used in practice can be evaluated.

The laser diode 11 or 12 is lit and controlled by a 1-dot lightingcontrol circuit 35. The 1-dot lighting control circuit 35 is equippedwith a clock pulse generator 36 for generating a clock pulse forclocking and a count circuit 37 for counting a clock pulse. Thesynchronous pulse of the synchronous sensor 27 is input to the 1-dotlighting control circuit 35.

The 1-dot lighting control circuit 35 and the drive control circuit 30are controlled by a control circuit 38 consisting of a personal computer(PC). The control circuit 38 is provided with an image processing inputboard 39. In this embodiment, the input board 39 employs an imageprocessing board with a three-input system, for example, an input systemfor red (R), green (G), and blue (B).

The first area-type imaging element 32 a is provided on a horizontalscanning start side. The third area-type imaging element 34 a isprovided on a horizontal scanning end side. The second area-type imagingelement 33 a is provided at a horizontal scanning center positionbetween the first and second area-type imaging elements 32 a and 34 a.The image outputs of the area-type imaging elements 32 a to 34 a arefetched in the control circuit 38 through the input board 39. Thecontrol circuit 38 has a computation circuit (computation means) 40 andan evaluation processing circuit 41.

As shown in FIG. 6, a reference pixel K is set as a coordinate originfor an arithmetic process from among the pixels of each of the area-typeimaging elements 32 a to 34 a. This reference pixel K is equivalent to apreviously designed writing reference position. The setting of thisreference pixel K will be described later. For now, assume that thedistance between the reference pixels K of adjacent area-type imagingelements 32 a and 33 a (33 a and 34 a) is set to L1. Also, assume that apreviously designed ideal image (beam spot S) which should be describedon a surface to be scanned is the one shown in FIG. 7. Referencecharacter R1 denotes the diameter of the ideal beam spot S.

The control circuit 38 has been calibrated so that the reference pixel Kis at the position of a coordinate origin. As shown in FIG. 8, thecomputation circuit 40 compute a scanning period T between the area-typeimaging elements from the distance L and a previously designed scanningspeed and also computes a scanning period t equivalent to 1 dot from thediameter R of the previously designed beam spot S measured in thescanning direction and the scanning period T. A signal representative ofthe scanning period T and the 1-dot scanning period t is input to thecount circuit 37 of the control circuit 35.

The scanning period T and the 1-dot scanning period t are determined bythe number of clock pulses output from the clock generator 36. If thecount circuit 37 counts the number of clocks equivalent to the scanningperiod T since the time the laser diode 11 or 12 was put out, the 1-dotlighting control circuit 35 will light the laser diode 11 or 12 being ina light-off state. Also, if the count circuit 37 counts the number ofclocks equivalent to the 1-dot scanning period t since the time thelaser diode 11 or 12 was lit, the 1-dot lighting control circuit 35 willput out the laser diode 11 or 12 being in a light-on state. In thissense, the scanning period T prescribes the light-off period of thelaser diode 11 or 12, i.e., a write timing period.

The laser diode 11 or 12 is controlled so as to light continuously bythe 1-dot control circuit 35 until a synchronous clock pulse from thesynchronous sensor 27 is input. If the synchronous clock pulse from thesynchronous sensor 27 is input, the laser diode 11 or 12 will be put outonce by the 1-dot lighting control circuit 35. If the scanning period Telapses, the laser diode 11 or 12 will be lit only for the 1-dotscanning period t by the 1-dot lighting control circuit 35 and again itwill be put out until the scanning period T elapses. If the scanningperiod T elapses, the laser diode 11 or 12 will be lit again for onlythe 1-dot scanning period t and then it will be put out. And if thesynchronous clock pulse of the second synchronous sensor 28 is input,the 1-dot lighting control circuit 35 will again light the laser diode11 or 12 after a return period (about 2T) to the scanning start side haselapsed.

In FIG. 8, the circular black mark represents the formation state of thebeam spot S (light-on state of the laser diode 11 or 12) equivalent to 1dot, while the circular white mark represents the non-formation state ofthe beam spot S (light-off state of the laser diode 11 or 12) equivalentto 1 dot.

Thus, if the laser-diode 11 or 12 is lit during a scanning periodequivalent to 1 dot during scanning by the 1-dot lighting controlcircuit 35, as shown in FIG. 9, beam spots S will be formed on thearea-type imaging elements 32 a to 34 a.

If the center positions O1, O2, and O3 of the beam spots S in thehorizontal scanning direction Q1 are computed with the evaluationprocessing circuit 41, the offset quantities d in the horizontaldirection Q1 with respect to the reference pixels K can be computed. Byway of example, FIG. 9 shows that the center position O1 on the writingstart side (image sensor 32 a) is offset to the right by X1, the centerposition O3 on the writing end side (image sensor 34 a) is offset to theright by X3, and that the offset quantity of the center position O2 atthe center position (imaging device 33 a) is d=X2=0.

If the center positions O1′, O2′, and O3′ of the beam spots S in thevertical scanning direction Q3 are computed with the evaluationprocessing circuit 41, the offset quantities d′ in the verticaldirection Q3 with respect to the reference pixels K can be computed. InFIG. 9 the offset quantities d′ in the vertical scanning direction ared′=0.

In FIG. 8, while it has been described that the distance L1 between thefirst area-type imaging element 32 a on the horizontal scanning startside and the second area-type imaging element 33 a at the centerposition is equal to the distance L1 between the third area-type imagingelement 34 a on the horizontal scanning end side and the secondarea-type imaging element 33 a at the center position, the presentinvention is not to be limited to this arrangement.

(Second Embodiment of the Evaluation Apparatus)

FIG. 10 shows a second embodiment of this evaluation apparatus. Thisevaluation apparatus employs a single image processing board as theinput board 39 and also evaluates offset quantities with respect to twopreviously designed writing reference positions. This evaluationapparatus is provided with an input board change-over switch 43. The1-dot lighting control circuit 35 controls the input board change-overswitch 43 so that an image is fetched from the third area-type imagingelement 34 a at the same time as the fetching of an image from the firstarea-type imaging element 32 a. Because the remaining constitution isidentical with the evaluation apparatus shown in FIG. 8, a detaileddescription thereof is not given by applying the same referencenumerals. FIG. 11 shows the control timing by the 1-dot lighting controlcircuit 35, and the scanning period (light-off period) T is computed bydividing the distance L2 between the area-type imaging elements 32 a and34 a with a previously designed scanning speed.

In this light beam characteristic evaluation apparatus, since the twoCCD cameras are spaced in the horizontal scanning direction, evaluationitems a through h, k, and m are evaluable. As a matter of course, ifthree CCD cameras are disposed as in the embodiment shown in FIG. 5,evaluation items a through k, and m are evaluable.

(Third Embodiment of the Evaluation Apparatus)

FIG. 12 shows a third embodiment of this evaluation apparatus. Thisevaluation apparatus employs a single image processing board as theinput board 39 and also evaluates an offset quantity with respect to asingle previously designed writing reference position.

This evaluation apparatus is provided with a single CCD camera 43. ThisCCD camera 43 is mounted on a movable body 45 installed on a guide shaft44 extending lengthwise in the horizontal scanning direction. Since themovable body 45 is controlled so as to reciprocate along the guide shaft44 by the control circuit 38, the CCD camera 43 can be set to a desiredwriting reference position.

In other words, when the CCD camera 43 is moved in the horizontalscanning direction, evaluation items a through f, k, and m can beevaluated at a desired position. Additionally, if a position of the CCDcamera 43 is set at the same position as that of the evaluationapparatus shown in FIGS. 5 and 10, evaluation items a through k, and mcan be evaluated in the same way.

If the distance from the synchronous sensor 27 to the CCD camera 43 isassumed to be L3 and if the distance L3 is divided by a previouslydesigned writing speed, the scanning period T (see FIG. 13) requiredfrom the synchronous sensor 27 to the reference pixel K of the area-typeimaging element 43 a of the CCD camera 43 can be computed.

Therefore, if the laser light source section Sou is put out during theperiod from the detection of the synchronous clock pulse by thesynchronous sensor 27 to the scanning period T and if the laser lightsource section Sou is lit during the 1-dot scanning period t by the1-dot lighting control circuit 35 at the same time as the elapse of thescanning period T, the laser spot S equivalent to 1 dot can be formed onthe area-type imaging element 43 a of the CCD camera 43 a duringscanning, as shown in FIG. 14.

The center position of the beam spot S of each evaluation apparatusmentioned above is obtained in the following way.

The pixels on the area-type imaging element 43 a are defined by Zij.Z1j, Z2j, . . . , Zij, . . . , and Znj mean pixels arranged in thehorizontal scanning direction Q1, while Zi1, Zi2, . . . , Zij, . . . ,and Zim mean pixels arranged in the vertical scanning direction Q3.Reference character i (integer from 1 to n) means the i-th point ascounted from the left, while reference character j (integer from 1 to m)means the j-th point as counted from the bottom.

Therefore, if the total sum Wj (Wj=Z1j+Z2j+Zij+Znj) of the signalsoutput from the pixels Z1j, Z2j, . . . , Zij, . . . , and Znj in thehorizontal scanning direction Q1 is computed in sequence from j=1 to j=min the vertical scanning direction Q3, as shown in FIG. 15, the lightbeam intensity distribution curve B1 in the vertical scanning directionQ3 can be computed. Similarly, if the total sum Wi (Wi=Zi1+Zi2+Zij+Zim)of the signals output from the pixels Zi1, Zi2, . . . , Zij, . . . , andZim in the vertical scanning direction Q3 is computed in sequence fromj=1 to j=n in the horizontal scanning direction Q1, as shown in FIG. 15,the light beam intensity distribution curve B2 in the horizontalscanning direction Q1 can be computed.

FIG. 16 is an example of the light beam intensity distribution curvecomputed in the aforementioned manner, the light beam intensitydistribution curve B2 in the horizontal scanning direction Q1 beingshown.

An evaluation processing circuit 41 sets a threshold value P1h to thelight beam intensity distribution curve B2, also specifies the addressesX1 and X2 of pixels in the horizontal scanning direction Q1 whichcorrespond to intensities traversing the threshold value P1h, andcomputes the address Xim of a pixel equivalent to the average value ofthe sum of the addresses X1 and X2. With this, the center position O1 ofthe light beam P1 in the horizontal scanning direction Q1 is computed.From the difference between this center position O1 and reference pixelK, the offset quantity of the center position O1 in the horizontalscanning direction Q1 is computed. By performing a similar process onthe light beam intensity distribution curve B1, the center position O1′of the light beam P1 in the vertical scanning direction Q3 is computedand the offset quantity d′ of the center position O1′ in the verticalscanning direction Q3 is also computed from the difference between thecenter position O1′ and reference pixel K.

Also, by computing the difference D between the addresses X1 and X2, thebeam diameter D of the light beam P1 in the horizontal scanningdirection Q1 is computed. The beam diameter D′ in the vertical scanningdirection Q3 is computed by performing a similar process on the lightbeam intensity distribution curve B1.

Note that the threshold value P1h used herein is set at a position of1/e (natural logarithm)2 from the peak Pmax.

As previously described, the center positions O1 and O1′ of the lightbeam P1 are computed based on the total sum of the output signals outputfrom the pixels Z1j, Z2j, . . . , Zij, . . . , and Znj arranged in thehorizontal scanning direction Q1 and the total sum of the output signalsoutput from the pixels Zi1, Zi2, . . . , Zij, . . . , and Zim arrangedin the vertical scanning direction Q3, respectively. However, thepresent invention is not limited to this method. For instance, bydescribing the light beam intensity distribution curves B1 and B2 frompixels near the peak Pmax and then computing the peaks of these beamintensity distribution curves B1 and B2 as the center of the light beamP1, the pixel corresponding to these peaks may be computed as the centerpixel of the light beam P1.

In addition, the output of each pixel has been quantized. Therefore, byexpressing a distribution of the quantized pixel outputs in athree-dimensional manner, pixels equivalent to the position of gravitymay be used as the center positions O1 and O1′ of the light beam P1 inthe horizontal scanning direction Q1 and vertical scanning direction Q3.

Note that even if the CCD camera 43 were arranged at a previouslydesigned reference writing position (i.e., at the position of imageheight O meaning the optical axis of the optical fθ system 23), anaccurate beam shape cannot be obtained if the beam diameter is measuredat a position slightly offset from the reference writing position. Forthis reason, the scanning period T shown in FIG. 13 is corrected basedon the offset quantity d, whereby the laser light source section Sou canalso be lit at the position of image height O.

(Fourth Embodiment of the Evaluation Apparatus)

FIG. 17 shows a fourth embodiment of this evaluation apparatus. In thisembodiment, there is provided a guide shaft 46 in a depth direction(i.e., optical-axis direction) Q4 crossing at a right angle with ahorizontal scanning direction Q1. A movable body 45 is provided so thatit can reciprocate along a guide shaft 44 in the horizontal scanningdirection Q1 and along the guide shaft 46 in the depth direction Q4.According to this constitution, the characteristics of a light beam canbe evaluated at a previously designed desired writing reference positionby employing a single CCD camera 43.

In the fourth embodiment, evaluation items a through k, and m can beevaluated and, in addition, evaluation item i can be evaluated becausethe CCD camera 43 is moved in the depth direction. Note that a movingmeans for moving the CCD camera 43 in the depth direction can beprovided in the evaluation apparatus shown in FIGS. 5, 10, and 12. Ifso, thee depth of evaluation item i can be evaluated also by the use ofthe evaluation apparatus shown in FIGS. 5, 10, and 12.

A proceeding direction (i.e., depth direction) Q4 of a light beam isevaluated in the following way.

As shown in FIG. 31(a), the CCD camera 43 is attached to the movablebody 45, and the movable body 45 is mounted on the guide shaft 44extending in the depth direction Q4. The movable body 45 is moved in thedepth direction Q4 of the light beam P1 successively at equal intervals,and the beam diameter D (see FIGS. 14 and 16) of the beam spot S of thelightbeam P1 issuessively calculated at each stopping position. Thus, abeam diameter curve (depth curve) Qm with respect to the depth directionQ4 can be obtained as shown in FIG. 31(b).

In this embodiment, the beam diameter curve Qm is calculated withrespect to the horizontal scanning direction Q1. However, a beamdiameter curve with respect to the vertical scanning direction Q3 may becalculated.

The position of the beam waist Bw is evaluated from this beam diametercurve Qm, and a beam waist position correction quantity ΔW is determinedfrom a previously designed desired writing reference position in thedepth direction Q4 and the evaluated position of the beam waist Bw.

FIG. 18 shows how the evaluation apparatus shown in FIG. 17 iscontrolled. The control circuit is first set to its initial state (step1) and then rotation of the pulse motor 29 is started (step 2). At thetime of the elapse of the time period which means that the pulse motor29 is assumed to have reached a steady revolution speed, the controlcircuit 38 outputs a signal toward the 1-dot lighting control circuit 35so that the laser diode 11 or 12 (laser light source section Sou) islit. On the other hand, the 1-dot lighting control circuit 35 detectswhether or not a synchronous clock pulse has been input from thesynchronous sensor 27 (step 4). When the synchronous clock pulse is notdetected after elapse of a predetermined period, the 1-dot lightingcontrol circuit 35 outputs an error occurrence signal toward the controlcircuit 38 (step 5). In response to the error occurrence signal, thecontrol circuit 38 outputs a signal toward the 1-dot lighting controlcircuit 35 so that the laser diode 11 or 12 (laser light source sectionSou) is put out (step 6). Based on the error occurrence signal, thecontrol circuit 38 stops rotation of the pulse motor 29 (step 7) andthen judges whether or not the measurement has ended (step 8).

In step 4, when the synchronous clock pulse is detected within apredetermined period, the 1-dot lighting control circuit 35 puts out thelaser diode 11 or 12 (laser light source section Sou) at the same timeas the synchronous clock pulse detection. At the time the count circuit37 has counted the number of clock pulses based on the scanning periodT, the 1-dot lighting control circuit 35 outputs a lighting signal whichcauses the laser diode 11 or 12 (laser light source section Sou) tolight for a period of 1 dot (step 9). The control circuit 38 obtains theimage of the beam spot S by this 1-dot lighting (step 10). Theevaluation processing circuit 41 performs an arithmetic process on thebasis of the image of the actually obtained beam spot S, therebyevaluating the characteristics required of the light beam P1 (step 11).And the evaluation processing circuit 41 outputs the result ofevaluation to a monitor (not shown) or storage means (not shown) (step12). Thereafter, the control circuit 38 outputs a signal toward the1-dot lighting control circuit 35 to put out the laser diode 11 or 12(laser light source section Sou) (step 6) and then stops drive of thepulse motor 29 (step 7). When measurements are repeated, steps 1 through12 are carried out again.

The characteristic evaluation of the light beam is performed byprocessing the center positions O1 and O1′, beam diameters D1 and D1′,and offset quantities d and d′ of the light beam P1.

By computing a ratio of beam diameters D1 and D1′, it can be evaluatedwhether the shape of the light beam P1 is an ellipse long in thehorizontal scanning direction Q1, or an ellipse near a circle, or anellipse long in the vertical scanning direction Q3.

(Detailed Structure of the Evaluation Apparatuses 1 to 4)

The following evaluation apparatus is presently being used as anembodiment.

FIGS. 35 and 36 show the mounted state of a write unit 1 onto an imageforming device. Reference numeral 100 denotes the base of the imageforming device. To this base 100 a write unit positioning member 101 isfixed as shown in FIGS. 35 and 36.

The write unit 1 has an exterior configuration shown in FIG. 37. Oneside wall of this write unit 1 is provided with positioning protrusions102 and 102, while the other side wall is provided with positioningholes 103 and 103. This write unit 1 is formed with a long and narrowslit hole 104′ extending in the horizontal scanning direction. From thislong and narrow slit hole 104′ a laser beam P1 is emitted toward aphotosensitive drum (not shown).

The write unit positioning member 101 has standing wall portions 104 and105 as shown in FIGS. 36, 38, and 39. The first standing wall portion104 is formed with a through hole 106, while the second standing wallportion 105 have positioning pins 107 rigidly attached thereto. Theexterior wall 108 of the second standing wall portion 105 constitutes asurface for positioning the write unit 1 in the horizontal scanningdirection. The point end portion of the write unit positioning member101 serves as a reference base attaching portion 109 as shown in FIG.39. Reference base attaching pins 110 are protruded from the referencebase attaching portion 109.

To this reference base attaching portion 109 a positioning referencebase 111 shown in FIGS. 40(a) through 40(d) is attached. Thispositioning reference base 111 extends lengthwise in the horizontalscanning direction. The upper surface of the positioning reference base111 is formed with positioning pins 112 and positioning block attachingholes 113. The lower portion of the positioning reference base 111 isformed with fitting holes 114 into which the reference base attachingpins 110 are fitted.

The upper surface of the positioning reference base 111 is inclined, andon this upper surface, standing plate portions 113 a are spaced andformed in the longitudinal direction. As shown in FIG. 41, a positioningblock member 115 is attached to the upper surface of the positioningreference base 111 and serves as an angular positioning determinationmember. In this embodiment, this positioning block member 115 hasstanding plate portions 116 and 117 and a flat plate portion 118 asshown in FIGS. 42(a) through 42(d). As shown in FIG. 41, an LD holderplate 119 as a cylindrical holder member is attached to the standingplate 116. The standing plate 116 is formed with a circular fitting hole120, and an engagement pin 121 is rigidly attached to the standing plate116. The second standing plate 117 is formed with an abutting portion117 a which is engaged by a CCD camera. The abutting portion 117 a isformed with a through hole 122. The circular fitting hole 120 isfinished into a precisely true circular shape.

The LD holder plate 119 is formed with a cylindrical boss portion 123 asshown in FIG. 43(a). The exterior shape of this cylindrical boss portion123 is also finished precisely. The cylindrical boss portion 123 isfitted into the circular fitting hole 120. The disc portion 119 a of theLD holder plate 119, as shown in FIG. 43(b), is formed with laser diodepositioning holes 124, later diode attaching holes 125, and angularpositioning determination engagement holes 126. In this embodiment, theangular positioning determination engagement holes 126 are providedaround the cylindrical boss portion 123 at intervals of 90 degrees.

As shown in FIG. 41, a reference laser diode (semiconductor laser) 127is attached to the LD holder plate 119 and serves as a reference laserlight source for determining a previously designed reference position.An attaching base 128 is fixed to the base 100, and a support base 129is fixed to the attaching base 128. The support base 129 is providedwith a slidable base 131. This slidable base 131 is provided with a CCDcamera unit 130. The CCD camera unit 130 is constituted by an attachingbase 131′ and a CCD camera 132. An abutting plate 131 a′ is stood up inthe attaching base 131′. A micrometer 133 is attached to the slidablebase 131. The micrometer 133 functions as adjustment means which adjuststhe imaging surface 130 a of the area-type imaging element so that theimaging surface 130 a is located at a surface equivalent to a surface tobe scanned. The point end portion of the CCD camera unit 130 abuts onthe abutting portion 117 a.

The slidable base 131 is formed with a bent plate portion 134 as shownin FIG. 35. The bent plate portion 134 is formed with an elongated hole135 extending in the sliding direction of the slidable base 131. The CCDcamera unit 130 is adjusted in the sliding direction by the micrometer133 so that the imaging surface of the area-type imaging element 130 ais located at the surface 31 equivalent to the surface of thephotosensitive drum to be scanned. Then, the CCD camera unit 130 islocked to the support base 129 by tightening the bent plate portion 134with a locking screw 136.

In this embodiment, three CCD camera units 130 are provided at regularintervals in the longitudinal direction of the positioning referencebase 111. As shown in FIG. 44, the interval is L10. In the figure, theleft CCD camera unit 130 is provided at the writing start side position.The middle CCD camera unit 130 is provided at the writing centerposition. The right CCD camera unit 130 is provided at the writing endside position.

As described in the first embodiment of the present invention, a laserlight source section Sou and an optical scanning system are providedinteriorly of the write unit 1. The surface of the photosensitive drumis scanned by this laser light source section, whereby writing isperformed.

As shown in FIG. 41, the center of the circular fitting hole 120 isaligned with a previously designed emission locus (emission line) Qn ofthe laser beam P1 in the horizontal scanning direction and verticalscanning direction. However, the reference laser light emitted from thereference laser diode 127 is not necessarily emitted along this emissionlocus Qn. Only emitting the laser light beam by itself cannot specifythe reference pixel K as the reference position of the area-type imagingelement 130 a present on the extension line of the emission locus Qnwith the reference laser light.

Hence, the reference laser diode 127 is first opposed to the CCD cameraunit 130 on the writing start side. As shown in FIG. 45(a), the LDholder plate 119 is fitted into the circular fitting hole 120. Then, theengagement pin 121 is fitted into one of the angular positiondetermination engagement holes 120 of the LD holder plate 119. Next, theLD holder plate 119 is rotated on the center of the circular fittinghole 120, whereby the circumferential wall 126 a of the angular positiondetermination engagement hole 126 of the LD holder plate 119 is broughtinto contact with the engagement pin 121 in the direction of rotation.With this, the angular positioning of the reference laser diode 127 isperformed.

And the reference laser diode 127 is lit with a lighting control circuit(not shown). The 1-dot lighting control circuit 35 of the write unit 1may be employed. At this time, assume that the emission direction of thelaser beam was a direction of Qm as shown in FIG. 44. Also, assume thatthe coordinates of the light-received pixel G of the area-type imagingelement 130 a which received the laser beam in the emission direction Qmwere x1 and y1 (G(x1, y1)). Next, as shown in FIG. 45(b), the fittingbetween the engagement pin 121 and the angular position determinationengagement hole 120 is released. Then, the LD holder plate 119 isrotated 180 degrees so that the engagement pin 121 is fitted into theangular position determination engagement hole 126′. Furthermore, thecircumferential wall 126′a of the angular position determinationengagement hole 126′ of the LD holder plate 119 is brought into contactwith the engagement pin 121 in the direction of rotation, whereby theangular positioning of the reference laser diode 127 is performed.

And the reference laser diode 127 is lit with a lighting control circuit(not shown). The 1-dot lighting control circuit 35 of the write unit 1may be employed. At this time, assume that the emission direction of thelaser beam was a direction of Qm′ as shown in FIG. 44. Also, assume thatthe coordinates of the light-received pixel G of the area-type imagingelement 130 a which received the laser beam in the emission directionQm′ were x2 and y2 (G(x2, y2)).

Hence, the coordinates K(X10, Y10) of the reference pixel K present onthe extension line of the emission locus Qn on the writing start sideare computed by the following equations:

 X 10={(x 1−x 2)/2}+x 2

Y 10={(y 1−y 2)/2}+y 2

Therefore, the position of the reference pixel K can be computed with ahigh degree of accuracy without employing a laser whose optical emissionaxis has been closely adjusted as the reference laser diode 127.

Next, a description will be made in the case of locating the positioningblock member 115 in opposition to the middle CCD camera unit 130 andcomputing the coordinates K(X12, Y12) of the reference pixel K presenton the extension line of a previously designed center emission locusQn′.

First, the reference laser diode 127 is opposed to the middle CCD cameraunit 130 and lit.

At this time, assume that the emission direction of the laser beam was adirection of Qm″. Also, assume that the coordinates of thelight-received pixel G of the area-type imaging element 130 a whichreceived the laser beam in the emission direction Qm″ were x3 and y3(G(x3, y3)).

The difference between the coordinates K(X12, Y12) of the referencepixel K present on the extension line of the emission locus Qn′ at thewriting center position and the coordinates K(X10, Y10) of the referencepixel K present on the extension line of the reference pixel on thewriting start side is equal to the difference between the coordinatesG(x3, y3) of the light-received pixel G of the area-type imaging element130 a which received the laser beam in the emission direction Qm″ andthe coordinates G(x2, y2) of the light-received pixel G of the area-typeimaging element 130 a which received the laser beam in the emissiondirection Qm′.

Therefore,

X 12−X 10=x 3−x 2

Y 12−Y 10=y 3−y 2

Hence,

X 12=X 10+x 3−x 2={(x 1−x 2)/2}+x 3

Y 12=Y 10+y 3−y 2={(y 1−y 2)/2}+y 3

Similarly, the coordinates K(X14, Y14) of the reference pixel K of theimage sensor 130 a of the CCD camera 132 provided on the writing endside are computed by the following equations with the coordinates of thelight-received pixel G as G(x5, y5):

X 14={(x 1−x 2)/2}+x 5

Y 14={(y 1−y 2)/2}+y 5

Therefore, once the coordinates of the reference pixel K of a certainCCD camera 132 has been specified by rotating the LD holder plate 119,the specification of the reference pixels K of the remaining CCD cameras132 can be performed without rotating the LD holder plate 119.

Note in FIG. 39 that the positioning block member 115 as an angularposition determination member is provided at the center position.

By moving the slidable base 131 in the longitudinal direction thereof bythe micrometer 133, it is possible to measure the beam diameter in thedepth direction.

In this embodiment of the present invention, although a singlepositioning block member 115 is relocated so that the reference pixel Kcan be computed at each position, a single positioning block member 115may be provided on the positioning reference base 111 so that it isslidable. Also, positioning block members 115 may be provided at thewriting start side position, writing center position, and the writingend side position, respectively.

(Variation)

FIGS. 46 through 51 show a variation of the aforementioned detailedstructure. FIGS. 46 through 48 show the attached state of a write unit 1to an image forming device. Columns 140 are stood up in a base 100. Tothe upper ends of the columns 140 a write unit positioning member 101 isfixed. In this variation, the write unit positioning member 101 isconstituted by a flat plate. The write unit positioning member 101 isformed with an opening 141 at the center thereof. The write unitpositioning member 101 is provided with three clamp devices 142. Eachclamp device 142 has a clamp lever 143. The write unit 1 is fixed to thewrite unit positioning member 101 by the clamp devices 142. An attachingbase 128 is fixed to the base 100. To the attaching base 128 a supportbase 129 is fixed. The support base 129 is provided with a slidable base131.

A CCD camera unit 130 is provided on the slidable base 131. The CCDcamera unit 130 is constituted by a CCD camera 132 and an attaching base131′. An abutting portion 131′a is stood up in the attaching base 131,and a micrometer 133 is attached to the slidable base 131. Themicrometer 133 fulfills a role of adjusting the imaging surface 130 a ofthe area-type imaging element so that the imaging surface 130 a islocated at a surface equivalent to a surface to be scanned.

As shown in FIG. 49, a clamp frame 144 is fixed to the support base 129.The slidable base 131 is formed with a guide hole 145 extending in thesliding direction of the slidable base 131. The slidable base 131 islocked to the support base 129 by tightening a locking screw 136.

As shown in FIG. 50, a positioning reference base 111 is attached to thewrite unit positioning member 101. This positioning reference base 111is fixed to the write unit positioning member 101 by the clamp device142. The lower portion of this positioning reference base 111 is formedwith an abutting portion 147. As shown in FIG. 51, a positioning blockmember 115 is attached to the upper portion of this positioningreference base 111.

The angular positioning block member 115 is formed with a circularfitting hole 120 and an engagement pin 121. To this angular positioningmember 115 an LD holder plate 119 is attached. To this LD holder plate119 a reference laser diode 127 is attached. The center of the circularfitting hole 120 is oriented in the same direction as a previouslydesigned emission locus Qn.

In this variation, when specification of the reference pixel K isperformed with the reference laser diode 127, the write unit 1 isremoved from the write unit positioning member 101 and then thereference laser diode 127 is set to the write unit positioning member101. When the laser light source of the write unit 1 is evaluated, thereference laser diode 127 and the positioning reference base 111 areremoved and the write unit 1 is set to the write unit positioning member101.

(Adjustment Apparatus Based on Evaluation Results)

A description will be hereinafter given of an adjustment apparatus basedon evaluation results of the evaluation apparatuses 1 to 4.

FIG. 20 relates to an adjustment apparatus based on the evaluation ofevaluation item a.

(Structure for Adjusting a Writing Position in the Horizontal Directionby the Movement of a Synchronous Sensor)

There is discussed the constitution of adjustment means for a writingstart position in the case where the beam center O1 of a beam spot S isoffset by ΔX in a horizontal scanning direction with respect toreference pixel K (writing reference position Z1) on a writing startside, as shown in FIG. 20.

In the case where the beam center O1 is offset by ΔX in a horizontalscanning direction Q1 with respect to the reference position Z1 on awriting start side, adjustment is performed by moving a synchronoussensor 27 in the horizontal scanning direction Q1 perpendicular to aprogressing direction of a light beam.

This synchronous sensor 27, as shown in FIG. 21, is attached to amovable body 47. The movable body 47 is provided on a guide shaft 48 sothat it is movable along the guide shaft 48, the guide shaft 48extending in the horizontal scanning direction Q1. The guide shaft 48 isextended between constitution walls 49 and 49′ constituting part of awrite unit 1. The constitution wall 49 is provided with an adjustingscrew 50, which in turn meshes with a screw portion 51 formed in theconstitution wall 49.

A tension spring 52 as an urging means is provided between the movablebody 47 and the constitution wall 49, the movable body 47 being urgedtoward the constitution wall 49. The point end portion 50 a of theadjusting screw 50 abuts on the wall portion of the movable body 47.

If the movable body 47 is moved slightly in the horizontal scanningdirection Q1 by rotating the adjusting screw 50 positively or reversely,as shown in FIG. 22, the distance L6 from the synchronous sensor 27 tothe writing reference pixel K (reference position Z1) will be adjusted,whereby the beam center O1 can be aligned with the previously designedwriting reference position Z1 in the horizontal scanning direction, andthe write timing correction of a writing start position becomespossible.

(Structure 1 for Adjusting a Writing Position in the Horizontal ScanningDirection by the Movement of the Write Unit or the Image Forming Unit)

Although the above-mentioned example performs the write timingcorrection of a writing start position by moving the synchronous sensor27 in the horizontal scanning direction, this variation performs theadjustment of write timing by moving a write unit 1 and an image formingunit 53 relatively in the horizontal scanning direction Q1.

FIG. 23 shows the positional relation between the write unit 1 and theimage forming unit 53. In this embodiment, at least the image formingunit 53 is provided with a developing roller unit 54, a transferringunit 55, and a charging unit 56 in the rotational area of aphotosensitive drum 25. Note that the transferring unit 55 and thecharging unit 56 may be formed integrally with each other. Also, thecleaning means and discharging means (not show) for the latent imagecarrier may be provided integrally with the image forming unit 53. Notethat the vertical scanning direction Q3 is perpendicular to the opticalaxis of a light beam cast on the photosensitive drum 25.

The main body constitution wall 57 of the image forming device, as shownin FIG. 24, is formed with guide holes 58 extending lengthwise in thehorizontal scanning direction Q1. The image forming unit constitutionwall 53 a constituting the image forming unit 53 is provided withprotruding support pins 53 b and a protruding boss portion 53 c. Theboss portion 53 c is formed with a screw portion 53 d. The support pins53 b are fitted in the guide holes 58, respectively.

The main body constitution wall 57 is provided with an adjusting screw59, which in turn meshes with the screw portion 53 d of the boss portion53 c. If the adjusting screw 59 is adjusted, the image forming unit 53will be moved in the horizontal scanning direction Q1 relatively againstthe write unit 1, whereby the position of the light beam P1 will beadjusted in the horizontal scanning direction Q1 with respect to theimage forming unit 53 (or the photosensitive drum 25). With thisadjustment, the write timing correction of the previously designedwriting start position is performed in the horizontal scanningdirection.

(Structure 2 for Adjusting a Writing Position in the Horizontal ScanningDirection by the Movement of the Write Unit or the Image Forming Unit)

In Structure 1, the image forming unit 53 is moved in the horizontalscanning direction Q1 by adjusting the adjusting screw 59 meshing withthe screw portion 53 d of the boss portion 53 c, whereby the position ofthe light beam P1 with respect to the image forming unit 53 is adjustedin the horizontal scanning direction Q1. However, in this variation, asshown in FIG. 25, the image forming unit 53 is mounted on a guide rail60 extending in the horizontal scanning direction Q1 and is movable inthe horizontal scanning direction Q1. The image forming unit 53 is urgedtoward the main body constitution wall 57 by an elastic member such as aspring 61. The adjusting screw 59 meshes with a screw portion 62 formedin the main body constitution wall 57. The point end portion 59 a of theadjusting screw 59 abuts on the image forming unit constitution wall 53a of the image forming unit 53.

If the adjusting screw 59 is rotated in a direction which weakens thepushing force of the point end portion 59 a of the adjusting screw 59 tothe image forming unit constitution wall 53 a, the image forming unit 53will be moved in a direction of arrow a1 by the urging force of thespring 61. On the other hand, if the adjusting screw 59 is rotated inthe opposite direction which increases the pushing force of the pointend portion 59 a of the adjusting screw 59 to the image forming unitconstitution wall 53 a, the image forming unit 53 will be moved in adirection of arrow a2 against the urging force of the spring 61 by thepushing force of the adjusting screw 59. With this movement, theposition of the light beam P1 with respect to the image forming unit 53is adjusted in the horizontal scanning direction Q1.

(Structure 3 for Adjusting a Writing Position in the Horizontal ScanningDirection by the Movement of the Write Unit or the Image Forming Unit)

In Structure 3, as shown in FIG. 26, the image forming unit 53 ismounted on the guide rail 60 extending in the horizontal scanningdirection Q1 and is movable in the horizontal scanning direction Q1. Inaddition, the image forming unit 53 is formed with a rack portion 63. Onthe other hand, the main body constitution wall 57 is provided with anadjusting shaft 64 having a control knob portion. The shaft portion ofthe adjusting shaft 64 is provided with a pinion 65, which in turnmeshes with the rack portion 63. The mesh between the pinion 65 and therack portion 63 makes it possible to move the image forming unit 53 inthe horizontal scanning direction Q1.

(Structure 4 for Adjusting a Writing Position in the Horizontal ScanningDirection by the Movement of the Write Unit or the Image Forming Unit)

As previously described, Structure 1 to Structure 3 have performed thepositioning of the light beam P1 to the image forming unit 53 by movingthe image forming unit 53 in the horizontal scanning direction Q1. But,this variation, as shown in FIG. 27, performs the positioning of thelight beam P1 to the image forming unit 53 by moving the write unit 1 inthe horizontal scanning direction Q1, while the image forming unit 53remains stationary. The main body constitution wall 57 is provided withguide holes 66 at places corresponding to the write unit 1, the guideholes 66 extending lengthwise in the horizontal scanning direction Q1.The write unit constitution wall 1 b is provided with protruding supportpins 67 and a protruding boss portion 68. The boss portion 68 is formedwith a screw portion 69, and the support pins 67 are fitted into theguide holes 66.

The main body constitution wall 57 is provided with an adjusting screw70, which in turn meshes with the screw portion 69 of the boss portion68. If the adjusting screw 70 is adjusted, the write unit 1 will bemoved in the horizontal scanning direction Q1 relatively against theimage forming unit 53, whereby the position of the light beam P1 will beadjusted in the horizontal scanning direction Q1 with respect to theimage forming unit 53.

(Structure 5 for Adjusting a Writing Position in the Horizontal ScanningDirection by the Movement of the Write Unit or the Image Forming Unit)

As previously described, Structure 1 to Structure 4 have performed thepositioning of the light beam P1 to the image forming unit 53 in thehorizontal scanning direction Q1 by providing the image forming unit 53downward and the write unit 1 upward. But, this variation performs thepositioning of the light beam P1 to the image forming unit 53 in thehorizontal scanning direction Q1 by providing the write unit 1 downwardand the image forming unit 53 upward.

As shown in FIG. 28, the image forming unit 53 is stationary, while thewrite unit 1 is mounted on a guide rail 71 extending in the horizontalscanning direction Q1 so that it is movable. The write unit 1 is urgedtoward the main body constitution wall 57 by a spring 72. The adjustingscrew 74 meshes with a screw hole 73 formed in the main bodyconstitution wall 57. The point end portion 74 a of the adjusting screw74 abuts on the write unit constitution wall 1 b.

If the adjusting screw 74 is rotated in a direction which weakens thepushing force of the point end portion 74 a of the adjusting screw 74 tothe write unit constitution wall 1 b, the write unit 1 will be moved ina direction of arrow a3 by the urging force of the spring 72. On theother hand, if the adjusting screw 74 is rotated in the oppositedirection which increases the pushing force of the point end portion 74a of the adjusting screw 74 to the write unit constitution wall 1 b, thewrite unit 1 will be moved in a direction of arrow a4 against the urgingforce of the spring 72 by the pushing force of the adjusting screw 74.With this movement, the position of the light beam P1 to the imageforming unit 53 is adjusted in the horizontal scanning direction Q1.

(Structure for Adjusting a Writing Position in the Horizontal ScanningDirection by the Movement of a Sheet Loading Position)

FIG. 52 shows a structure for adjusting a writing position by moving asheet loading position in the horizontal scanning direction Q1.

In this embodiment, as shown in FIG. 52(a), side race LED1 to LEDn areprovided so that they face the surface 26 of the photosensitive drum 25.The LED1 to LEDn are arranged in a direction corresponding to thehorizontal scanning direction Q1 as shown in FIG. 52(b).

The LED1 to LEDn are lit and controlled according to sheet size. TheseLED1 to LEDn are employed according to sheet size so that developingtoner does not adhere to the side race of the photosensitive drum 25(conveyance direction(vertical scanning direction Q3)). In other words,the LED1 to LEDn are employed to exposure the opposite end portions ofthe photosensitive drum 25.

The image forming unit 53 is provided with sheet loading trays 100 and101. To the sheet loading tray 100 a side guide fixing plate attachingportion 102 is attached. This side guide fixing plate attaching portion102 is provided with a side guide fixing plate 103. To this side guidefixing plate 103 a side guide 104 is attached so that it is slidableaccording to sheet size. The sliding direction of the side guide 104corresponds to the horizontal scanning direction (perpendicular to asheet conveying direction).

The side guide fixing plate 103 is slidable against the side guidefixing plate attaching portion 102 in the same direction as the sideguide 104. The side guide fixing plate 103 is provided with an elongatedhole 105 so that a writing position can be adjusted based on a writingposition correction quantity based on the evaluation results of thefirst to the fourth evaluation apparatuses. Memory corresponding to thewriting position correction quantity is provided within this elongatedhole 105. After this adjustment, the side guide fixing plate 103 isfixed to the side guide fixing plate attaching portion 102 by screws.

For example, in the case of a sheet of A3 size long sideways, LED1,LED2, LEDn−1, and LEDn are lit by a CPU. In the case where a writingposition must be corrected in the horizontal scanning direction Q1 by aquantity equivalent to a single LED (in FIG. 52(b), when a writingposition is offset upward), LED lighting control for each size isshifted by that quantity and executed. In the case of a sheet of A3 sizelong sideways, LED1, LEDn−2, LEDn−1, and LEDn are lit.

That is, if a writing position is moved and adjusted in the horizontalscanning direction Q1, it will be sufficient if a sheet conveyingdirection is moved. Furthermore, during conveyance of a sheet to thephotosensitive drum 25, the sheet may be slid in the horizontal scanningdirection Q1 while being conveyed.

(Structure for Adjusting a Writing Position in the Vertical ScanningDirection by the Movement of the Write Unit or Image Forming Unit)

This adjustment structure performs adjustment along the verticalscanning direction perpendicular to the traveling direction andhorizontal scanning direction Q1 of a light beam which is emitted fromthe write unit and incident on the photosensitive drum, based on theresult of the evaluation (evaluation item b) of a writing position inthe vertical scanning direction shown in FIG. 29, obtained by the firstto the fourth evaluation apparatuses.

That is, this positional adjustment structure adjusts write timing bymoving the write unit 1 and the image forming unit 53 relatively in thevertical scanning direction Q3.

That is, this adjustment structure relates to the adjustment means ofthe writing start position when the beam center O1′ of the beam spot Sis offset by ΔY in the vertical scanning direction Q3, as shown in FIG.29.

The main body constitution wall 57, as shown in FIG. 30, is providedwith an adjusting screw 75 constituting part of a moving means and isformed with guide holes 76 extending in the vertical scanning directionQ3. The write unit 1 is provided with support pins 77 and is formed witha boss portion 78. The boss portion 78 is formed with a screw portion79. The adjusting screw 75 meshes with the screw portion 79 of the bossportion 79. If the adjusting screw 75 is adjusted, the write unit 1 willbe moved in the vertical scanning direction Q3 relatively against theimage forming unit 53. With this movement, the position of the lightbeam P1 is adjusted in the vertical scanning direction Q3 with respectto the image forming unit 53.

In this adjustment structure, although the position of the light beam P1is adjusted in the vertical scanning direction Q3 with respect to theimage forming unit 53 by moving the write unit 1 in the verticalscanning direction Q3, the position of the light beam P1 to the imageforming unit 53 may be adjusted by moving the image forming unit 53 inthe vertical scanning direction Q3. In this case, the image forming unit53 is formed with support pins 76 and a boss portion 78 which constitutepart of a moving means.

In addition, the moving means may be constituted by a pinion which isrotated by an adjusting shaft with a control knob portion, and a rackmeshing with this pinion.

(Structure for adjusting a depth by a laser diode (LD) unit)

Based on the appropriate beam waist correction quantity ΔAW obtained inthe depth evaluation, the fourth embodiment of the present inventionmoves the collimator lens 13 and 14 along the optical path of the lightbeam P1, thereby adjusting the optical path length. The optical pathlength adjustment means will hereinafter be described in reference toFIG. 32.

A base 81 for attaching the laser diode 11 (12) is fixed to the writeunit constitution wall 1 b by means of screws 82. This attaching base 81is provided with an attaching hole 83 for the laser diode 11 (12) and anattaching hole 84 for the collimator lens 13 (14). The laser diode 11(12) is fitted into the attaching hole 83 and fixed. The collimator lens13 (14) is held by a lens barrel 85. The outer circumferential portionof the lens barrel 85 is formed with a male screw portion 86. The innercircumferential wall of the attaching hole 84 is formed with a femalescrew portion 87. The male screw portion 86 of the lens barrel 85 mesheswith the female screw portion 87 of the attaching base 81. With thisarrangement, the lens barrel 85 is held by the attaching base 81 so thatit is movable in the axial direction of the attaching base 81.

The positional adjustment of the beam waist Bw is performed by rotatingthe lens barrel 85. That is, it is done by moving the collimator lens 13(14) in the optical axis direction Q5 of the collimator lens 13 (14)with respect to the laser diode 11 (12). After adjustment of this beamwaist Bw, the lens barrel 85 is fixed to the attaching base 81, forexample, by an adhesive agent.

(Depth Adjusting Structure 1 for Adjusting a Depth by the Write Unit orthe Image Forming Unit)

The aforementioned example has adjusted the beam waist by moving thecollimator lens 13 and 14 in the optical axis direction. This variation,as shown in FIG. 33, is provided with guide holes 88 a and screwattaching portions 88 b extending in the height direction of the mainbody constitution wall 57. The write unit constitution wall 1 b isprovided with guide pins 89, which are loosely fitted into the guideholes 88 a. The write unit 1 is urged upward by the urging force oftension springs 90 through the guide pins 89. On the other hand, thescrew attaching portions 88 b are provided with screw portions 92, whichin turn mesh with adjusting screws 91. The point end portion 91 a of theadjusting screw 91 abuts on the guide pin 89. If the adjusting screws 91are rotated to adjust the gap between the write unit 1 and the imageforming unit 53, the optical path length will be varied and thereforethe position of the beam waist is adjusted with respect to the surface26 of the photosensitive drum 25.

(Depth Adjusting Structure 2 for Adjusting a Depth by the Write Unit orthe Image Forming Unit)

The first depth adjusting structure is provided with the adjustingscrews 91 to adjust the gap between the write unit 1 and the imageforming unit 53. In a second depth adjusting structure, as shown in FIG.34, the main body constitution wall 57 is provided with an adjustingknob 94. The shaft portion 95 of the adjusting knob 94 is provided withan eccentric cam 96. On the other hand, the write unit 1 is providedwith an abutting portion 97, which in turn abuts on the cam surface 96 aof the eccentric cam 96. The abutting portion 97 is brought into contactwith the cam surface 96 a by tension springs 90 each provided between astop pin 93 and a guide pin 89. If the optical path length between thewrite unit 1 and the image forming unit 53 is changed by rotating theadjusting knob 94, the positional adjustment of the beam waist can beperformed with respect to the surface 26 of the photosensitive drum 25.

Note that the aforementioned optical path length adjustment means may beconstituted by a pinion which is rotated by an adjusting screw, and arack meshing with this pinion.

In this example, although the write unit 1 is moved in the verticalscanning direction, the image forming unit 53 may be moved.

(Adjustment Based on Evaluation Results Regarding the Other EvaluationItems)

a) When the evaluation in the evaluation item c or d is outside anallowable range, it is considered that the polygon mirror 19 isdefective, so it is desirable to exchange the polygon mirror 19 mountedin the write unit 1 for a new one.

b) When the evaluation in the evaluation item e or f is outside anallowable range, the aperture diameter of an aperture member (notshown), provided in an optical path between the laser diode LD and thepolygon mirror 19, is adjusted. This aperture member is usually arrangeddirectly after the collimator lens in the traveling direction of a lightbeam. In this adjustment of the aperture diameter of the aperturemember, the aperture diameter of the aperture member may be adjusted bymechanical adjustment means. Also, the aperture member presentlyarranged in the optical path may be removed and exchanged for anaperture member having another aperture diameter.

c) It is desirable that the adjustment based on the evaluations of themagnification error and magnification error deviation in the evaluationitems g and i be performed by an exchange of fθ lens or an exchange ofreflecting mirrors.

This is because there is a high possibility that a magnification erroror magnification error deviation will occur as a result of the influenceon the right and left optical path lengths caused by an optical defectin optical elements such as the fθ lens 24 and the reflecting mirror 24constituting an optical system which guides the light beam reflected bythe polygon mirror 19 to the photosensitive drum 25.

In the case of only the magnification error in the evaluation item g, asshown in FIG. 53(a), the adjustment can be performed by adjusting thereflecting mirror 24 or fθ lens 23 around the optical axis O 10 througha predetermined angle.

(d) For adjustment based on the evaluations of the scanning line tiltand scanning line curvature in the evaluation items h and j, it is alsodesirable that the adjustment be performed by an exchange of fθ lens oran exchange of reflecting mirrors.

This is because there is a high possibility that scanning line tilt orscanning line curvature will occur as a result of the influence on theright and left optical path lengths caused by an optical defect inoptical elements such as the fθ lens 24 and the reflecting mirror 24constituting an optical system which guides the light beam reflected bythe polygon mirror 19 to the photosensitive drum 25.

In the case of only the scanning line tilt in the evaluation item h, asshown in FIG. 53(b), the adjustment can be performed by adjusting thereflecting mirror 24 or fθ lens 23 around the optical axis O 10 througha predetermined angle and also adjusting the inclined angle of thereflecting mirror 24 in a direction of arrow O 11.

(e) Adjustment based on the evaluation of the pitch space in theevaluation item m is performed by adjusting a unit with a plurality ofLDs around the optical axis through a predetermined angle.

(f) Adjustment based on the evaluation of the scanning period in theevaluation item i is performed by adjusting the rotation speed of thepolygon mirror 19. As with FIG. 53(a), the scanning period can also beperformed by adjusting the reflecting mirror 24 or fθ lens 23 around theoptical axis O 10 through a predetermined angle.

(g) Adjustment based on the evaluation of the depth in the evaluationitem 1 is performed as described in FIGS. 32 to 34.

While the present invention has been fully described with relation tothe preferred embodiment thereof, the invention is not to be limited tothe details given herein, but may be modified within the scope of theappended claims.

What is claimed is:
 1. An adjustment method comprising the steps of:providing a write unit incorporating an optical scanning system to forman electrostatic latent image on a surface of a latent image carrier bya light beam emitted from a laser light source; evaluating an offsetquantity of said light beam in a horizontal scanning direction bylighting said light beam for a scanning period equivalent to 1 dot andevaluating a beam center of said 1 dot light beam with respect to areference pixel to determine the offset quantity; and moving said writeunit relatively in said horizontal scanning direction against saidlatent image carrier in correspondence to the offset quantity of saidlight beam in said horizontal scanning direction, thereby adjusting saidwrite unit.
 2. An adjustment method comprising the steps of: providing awrite unit incorporating an optical scanning system to form anelectrostatic latent image on a surface of a latent image carrier by alight beam emitted from a laser light source; evaluating an offsetquantity of said light beam in a horizontal scanning direction bylighting said light beam for a scanning period equivalent to 1 dot andevaluating a beam center of said 1 dot light beam with respect to areference pixel to determine the offset quantity; and moving said writeunit relatively in said horizontal scanning direction against an imageforming unit incorporating at least said latent image carrier incorrespondence to the offset quantity of said light beam in saidhorizontal scanning direction, thereby adjusting said write unit.
 3. Anadjustment method wherein an evaluation system evaluates an offsetquantity of a light beam in a vertical scanning direction and a writeunit, incorporating an optical scanning system to form an electrostaticlatent image on a surface of a latent image carrier by the light beamemitted from a laser light source by lighting said light beam for ascanning period equivalent to 1 dot and evaluating a beam center of said1 dot light beam with respect to a reference pixel to determine theoffset quantity, is adjusted by moving said write unit relatively in avertical scanning direction against said latent image carrier incorrespondence to the offset quantity of the light beam in said verticalscanning direction, the vertical scanning direction being defined as adirection perpendicular to both a traveling direction of a light beamwhich is incident from said write unit toward said image forming unitand a horizontal direction.
 4. An adjustment method wherein anevaluation system evaluates an offset quantity of a light beam in avertical scanning direction and a write unit, incorporating an opticalscanning system to form an electrostatic latent image on a surface of alatent image carrier by a light beam emitted from a laser light sourceby lighting said light beam for a scanning period equivalent to 1 dotand evaluating a beam center of said 1 dot light beam with respect to areference pixel to determine the offset quantity, is adjusted by movingsaid write unit relatively in a vertical scanning direction against animage forming unit incorporating at least said latent image carrier incorrespondence to the offset quantity of the light beam in said verticalscanning direction, the vertical scanning direction being defined as adirection perpendicular to both a traveling direction of a light beamwhich is incident from said write unit toward said image forming unitand a horizontal direction.
 5. An adjustment method wherein at leasteither an image forming unit or a write unit is moved so that a spacetherebetween is increased or decreased, in order to adjust an opticalpath length between a laser light source and a writing object surface ofsaid image forming unit and based on a beam waist position correctionquantity obtained by a light beam characteristic evaluation methodcomprising the steps of: (a) lighting said laser light source of a lightbeam which is employed to scan said writing object surface of said imageforming unit linearly during a scanning period equivalent to 1 dot; (b)moving an area-type solid-state imaging element which detects said lightbeam in order along the traveling direction of said light beam with saidwriting object surface as a reference position, thereby obtaining a beamimage at each position by said area-type solid-state imaging element;(c) based on each beam image obtained by said area-type solid-stateimaging element at each position in a traveling direction of said lightbeam, computing a beam diameter at said each position of said light beamand thereby computing a beam diameter with respect to a depth direction;(d) from said beam diameter and a depth, computing a depth curverepresentative of a relation of said beam diameter to said depth; (e)specifying a beam waist position on the basis of said depth curve; and(f) from a difference between said beam waist position and saidreference position, computing said beam waist position correctionquantity.
 6. An adjustment method wherein an optical path length betweena laser light source and a surface to be scanned is adjusted based on abeam waist position correction quantity obtained by a light beamcharacteristic evaluation method comprising the steps of: (a) lightingsaid laser light source of a light beam which is employed to scan saidsurface linearly during a scanning period equivalent to 1 dot; (b)moving an area-type solid-state imaging element which detects said lightbeam in order along a traveling direction of said light beam with saidwriting object surface as a reference position, thereby obtaining a beamimage at each position by said area-type solid-state imaging element;(c) based on each beam image obtained by said area-type solid-stateimaging element at each position in the traveling direction of saidlight beam, computing a beam diameter at said each position of saidlight beam and thereby computing a beam diameter with respect to a depthdirection; (d) from said beam diameter and a depth, computing a depthcurve representative of a relation of said beam diameter to said depth;(e) specifying a beam waist position on the basis of said depth curve;and (f) from a difference between said beam waist position and saidreference position, computing said beam waist position correctionquantity.